The Messenger

No. 149 – September 2012 Progress on SPHERE on Progress comb a laser frequency with HARPS Calibrating galaxies early-type Disentangling ALMA with mm-VLBI Planning Telescopes and Instrumentation

Astronomical Spectrograph Calibration at the Exo-Earth Detection Limit

Gaspare Lo Curto1 length (such as in Å), as a fractional For the measurement of frequencies, Luca Pasquini 1 wavelength, e.g. 10–7, or by scaling by the LFCs represent the ultimate level of preci- Antonio Manescau1 speed of light to express it in m/s. The sion, as they are locked to the energy Ronald Holzwarth 2, 3 limitation on Th-Ar wavelength precision level of a well-known atomic transition via Tilo Steinmetz 3 is due not only to the measurement pro- an atomic clock. They are the most pre- Tobias Wilken 3 cess (Palmer Engleman, 1983), but also cise time-keeping devices, and the unit of Rafael Probst 2 to the production method (contamination) measurement of time in the International Thomas Udem 2 and aging of the lamps. Even when aver- System (SI), the second, is defined by the Theodor W. Hänsch 2 aging over a wide spectrum with say, caesium transition via a caesium atomic Jonay González Hernández 4, 5 10 000 lines, measurements are limited clock. LFCs have many applications, from Massimiliano Esposito 4, 5 to an overall precision of 10–9 at best metrology and precise time-keeping to Rafael Rebolo4, 5 (the achievable precision is furthermore laboratory atomic and molecular spec- Bruno Canto Martins 6 degraded by line blending, and non- troscopy. Now the period is beginning Jose Renan de Medeiros 6 uniform density of the Th lines across the when LFCs will “look at the sky”. spectrum).

1 ESO This precision in the measurement of the The demonstrator programme 2 Max-Planck-Institut für Quantenoptik, positions of spectral lines is not sufficient Garching, Germany for various compelling science cases: In 2006 ESO approached the group of 3 Menlo Systems GmbH, Martinsried, – the measurement of the variation of the Prof. Theodor Hänsch at the Max Planck Germany fundamental constants, which requires Institute for Quantum Optics (MPQ), to 4 Instituto de Astrofisica de Canarias, a precision at least as good as the study the possibility of using an LFC for La Laguna, Spain precision with which the constants are the calibration of high-resolution astro- 5 Departamento de Astrofísica, determined; for the best known (the nomical spectrographs. Due to its unsur- Universidad de La Laguna, Tenerife, proton to electron mass ratio and the passed stability, HARPS at the 3.6-metre Spain fine structure constant) this is telescope in La Silla provided the best 6 Universidade Federal do Rio Grande de ~ 3–4 × 10–10 (Beringer et al., 2012); candidate to validate the performance of Norte, Natal, Brazil – the amplitude of the recoil motion this technique (Mayor et al., 2003). A fruit- imprinted by the Earth on the Sun ful collaboration was initiated between is ~ 9 cm/s. The radial velocity detec- ESO, MPQ and Menlo GmbH, a spin-off Following the development of the laser tion of an extrasolar planet with company from MPQ which markets LFCs, frequency comb which led to the 2005 the mass of the Earth in a 1 AU orbit with the goal of demonstrating the feasi- Nobel Prize in Physics, we began in around its solar-type star therefore bility of operating an LFC to calibrate an vestigating the possibility of using this requires a measurement precision of astronomical spectrograph, thus opening novel technology for precise and accu- about 3 cm/s, or 10–10; up a new horizon for the current and next rate spectrograph calibration. A pro- – the direct measurement of the expan- generation high-precision, high-resolution gramme was begun, aimed at demon- sion rate of the Universe, which can spectrographs. strating the capabilities of laser fre- constrain the cosmological parameters quency combs (LFC) when coupled to that define the metric of the theory The demonstrator programme started in an astronomical spectrograph. In the of gravity, requires a measurement pre- 2007 (Araujo-Hauck et al., 2007) and last three years we have tested an LFC cision at the level of cm/s (10–10) for concluded in 2011. In this period a proto- connected to HARPS at the 3.6-metre over ten years (Liske et al., 2008). type LFC dedicated to astronomy (or telescope in La Silla, the most precise astro-comb) was developed and refined. spectrograph available. Here we show The new class of giant telescopes with The astro-comb was tested in the labora- the very promising results obtained so greatly increased light-collecting power tory; in the infrared (IR) regime on a tele- far, and outline future activities, including will naturally ease the photon noise limi scope for the first time (Steinmetz, 2008); the provision of an LFC system for rou- tation to high precision spectroscopy by to validate technical solutions; and in four tine operation with HARPS, to be offered a factor of five to ten. A new calibration campaigns in the visible, with HARPS to the community in the near future. source is therefore needed, which ena- at the 3.6-metre telescope in La Silla, to bles these science cases and capitalises test the global performance (Lo Curto on the great opportunity that giant tele- et al., 2010; Wilken et al., 2010; Wilken et The most widely used wavelength refer- scopes open up for high precision spec- al., 2012). ence in astronomical spectroscopy, the troscopy. The ideal calibration source thorium–argon (Th-Ar) lamp, can achieve would be at least ten times more precise An LFC consists of thousands of equally a precision on the determination of indi- than Th-Ar lamps allow and would have spaced frequencies over a bandwidth vidual line positions of several tens of many unblended lines, with approximately of several THz. It is based on the proper- metres per second (m/s). The uncertainty the same intensity and equally spaced ties of femtosecond (fs) mode-locked in the wavelength of a spectral line can across the spectrum. The obvious choice lasers. The frequency difference between either be expressed as an absolute wave- is the laser frequency comb. two neighbouring lines corresponds to

2 The Messenger 149 – September 2012 Figure 1. The spectrum of the LFC dispersed by a Although an LFC based on fibre lasers are detrimental to nonlinear conversion low-resolution grating and projected on a wall. The is essentially an off-the-shelf product, its processes. The approach to overcome individual lines are not resolved and only the continuum is visible: its spectral structure is due to the adaptation for use in an instrument like this dilemma employs two key compo- spectral broadening stage and can be flattened out HARPS requires major developments. nents. First, a comb system based on by a spatial light modulator (SLM). The basic turn-key LFC systems available an Yb-fibre laser enables the use of Yb- on the market today deliver a comb of fibre high-power amplifiers to reduce the repetition frequency (frep) of the lines centred at 1025–1050 nm, with a re the problem of low pulse energies. Sec- pulsed laser and is therefore constant petition frequency of 250 MHz and gen- ond, when using specially designed across the comb spectrum. The entire erally cover only few nanometres in wave- photonic crystal fibres (PCFs), relatively LFC spectrum can be described by the length. Resolving spectral lines 250 MHz low pulse energies are sufficient to obtain simple equation f = foff + n∙frep where frep apart in the visible range requires a spec- spectral broadening. is the repetition frequency, i.e. the dis- tral resolution of more than six million, tance in frequency between two adjacent which is not practical for the typical use Another challenge comes at the FPC fil- lines, and foff is the “offset frequency” that of an astronomical spectrograph. An LFC tering stage and arises from the fact that can be interpreted as a “zero point”; n with such a line spacing would appear the nonlinear processes (interactions is a large integer which projects the radio as a continuum source to instruments between photons) in the PCF can amplify frequencies foff and frep into the visible such as HARPS or UVES (see Figure 1). spectral lines that were intended to be domain. Since all frequencies used in the suppressed. We saw this effect during system are radio frequencies, they can New developments are needed to oper- our first test run in La Silla. The solution be stabilised to an atomic clock using ate an LFC on an astronomical spectro- was to employ more FPC cavities, essen- well-established electronic phase-locking graph in the visible with a spectral resolu- tially one of them replicating the sup techniques. In this way, each optical tion of ~ 105: pression of the unwanted modes, and frequency obtains the accuracy and long- 1) increase the repetition frequency to with a higher finesse. Finally in our system term stability of the atomic clock. ~ 18 GHz; we used three FPCs in series to guar 2) double the frequency of the spectrum antee a sufficient suppression of the An LFC acts like a gear, transferring the to have it centred in the visible at intermediate lines. A series of four FPCs precision of atomic clocks from the micro- ~ 520 nm; was also tested, but no improvements wave regime to the optical. LFCs are 3) broaden the spectrum to increase were noticed from the fourth cavity. The the ideal calibrator for astronomical spec- wavelength coverage. line spacing is increased to 18 GHz, trographs if they can cover the spectral These are the three steps where most of which is well resolved by HARPS (the in bandwidth of the spectrograph with a the efforts of the programme have been strument has an intrinsic resolution of sufficiently flat spectrum and if their line focussed. ~ 5 GHz). spacing is adapted to the spectrograph’s resolution. While there are several pro- After the last FPC a fibre amplifier is posed frequency comb systems that will Towards an LFC for astronomy employed that can deliver up to 10 W to match the criteria for a spectrograph cali- facilitate the subsequent nonlinear pro- brator, our choice has been to use a High finesse Fabry-Pérot cavities (FPCs) cesses. The spectral bandwidth after fibre-laser-based LFC. Fibre lasers are acting as periodic, high-resolution spec- these amplifiers suffers from re-absorp- technically mature and turn-key systems tral filters can be used to increase the tion and gain narrowing. The initial 50 nm that are commercially available. When line spacing by transmitting only modes wide spectrum reduces to a 3 dB band- using Yb-fibre lasers, high-power amplifi- (lines) that are phase-shifted by an inte- width of only 20 nm after the high-power ers can be employed and the second ger number of wavelengths and sup- amplifier. After re-amplification, the fre- harmonic of the central wavelength pressing the intermediate ones. After this quency of the light is doubled by a sec- (1030 nm) is in the centre of the desired first step, the spectrum of the LFC under- ond harmonic generator (SHG), and wavelength range for a spectrograph goes two nonlinear processes: one for finally injected into the PCF for spectral in the visible. However, the required fibre frequency doubling and one for spectral broadening. The broadening is a highly length limits the round-trip time in the broadening. The challenge is to combine nonlinear process (four-wave mixing), and oscillator, and thus the line spacing of the the frequency conversion and the high so the intensity distribution in the final laser (its pulse repetition rate) is currently pulse repetition rate. A high repetition rate spectrum can vary. For this reason, in the limited to roughly below 1 GHz. corresponds to low pulse energies that last test run, a spatial light modulator

The Messenger 149 – September 2012 3 Telescopes and Instrumentation Lo Curto G. et al., Spectrograph Calibration at the Exo-Earth Detection Limit

Figure 2. Representa- Rb atomic tion of the HARPS-LFC clock Fabry-Pérot setup as described in 18 GHz filter cavities the text. The SLM after 250 MHz the PCF is missing in the figure because it Laser frequency comb was not always used during data acquisition (see text for details). High power From Wilken et al., 2012. Dynamic fibre amplifier scrambler PCF HARPS A 450 nm–590 nm Fibre 1040 nm–1060 nm SHG spectrograph coupling B Multimode fibre Single mode fibre

Figure 3. A comparison LFC spectrum of a portion of one order of the LFC and the Th-Ar lamp as seen by HARPS. Th-Ar lamp spectrum

(SLM) was sometimes inserted as a last The wavelength range of the LFC for are considering a test with two independ- stage of the LFC, yielding a flat spectrum HARPS now covers ~ 100 nm, and work ent LFCs feeding light to HARPS in the envelope at the cost of an attenuation of is in progress to extend this to at least future. Currently we are focussing instead 12 dB. 200 nm. Owing to the high line density of on effects due to mode (mis)matching, the LFC spectra, we are now able to coupling and injection. To characterise Light from the LFC is finally coupled to a better characterise the detectors. For these, we inject light into both HARPS multimode fibre that comprises a dynamic example, Figure 4 shows the effect of the calibration fibres and illuminate both the mode scrambler. Multimode fibres are stitching pattern of the CCD fabrication object and the simultaneous reference mandatory, because starlight cannot yet on the wavelength calibration. Every orders (from here onward referred to be coupled efficiently to single mode 512 pixels the wavelength solution en as channels) in the CCD. We then moni- fibres. The scrambler serves to reduce counters a discontinuity as the intra-pixel tor the relative drifts measured between multi-pass interference effects and the distance is slightly different along the the two channels, with the assumption sensitivity to the light injection by aver stitching borders. The effect reaches over that instrumental drifts are subtracted out aging over a large number of fibre modes. 60 m/s, well above the attainable stability when looking at the relative variations The light is then coupled, within the of HARPS. Although the effect is clearly between them (an assumption which is HARPS calibration unit, to the two HARPS visible when using the LFC calibration, it the basis of the simultaneous reference calibration fibres, which simultaneously goes unnoticed when Th-Ar calibration method). illuminate the telescope focal plane, is used, due to the low number of lines injecting light into the “object” fibre and present in the orders and their highly non- In Figure 5 the measured drift of all the the “simultaneous reference” fibre. The uniform distribution. This effect clearly spectra collected in the two test runs of system is sketched in Figure 2. underlines the need for a detailed char- November 2010 and January 2011 is acterisation of the detector when the shown. During the test run we stressed highest radial velocity precision and ac the system in many ways, well beyond Characterising the LFC on HARPS curacy are aimed for. Such in-depth char- what could be considered “standard acterisation can be performed with the operation”: we completely disassembled Some of the advantages of LFCs over use of the LFC, by modifying the param the FPC chain and reassembled it again Th-Ar lamps are immediately noticeable eters that define the spectrum, i.e. the in January to test a fourth FPC; changed from Figure 3, where a portion of the offset frequency and the repetition fre- several PCFs; inserted and removed order of the two sources is compared. quency, effectively scanning the detector neutral density filters; misaligned the The LFC has a very dense, non-blending and probing all the pixels which lie within injection fibres; introduced polarimetric line pattern (~ 350 lines per order), which the spectral profile. plates, integrating spheres, etc.... We also is also very uniform in intensity. In con- switched off the CCD cooling for few trast the Th-Ar lamp has fewer lines The characterisation of the stability of minutes. Despite this, each individual (~ 100 lines per order), some of which the LFC system when coupled to HARPS series of data shows a relative drift con- are saturated. The spectra in Figure 3 has been clearly the first priority during sistent with, or very close to, the esti- were obtained using both the object and the tests. However with only one comb mated photon noise, and the relative drift the simultaneous reference fibres of available we have to rely on its intrinsic between the two channels never HARPS, and by illuminating the spectro- stability as verified up to now on very exceeded 1 m/s, and the root mean graph simultaneously with both sources. many laser physics experiments. We square (RMS) of the relative drift was

4 The Messenger 149 – September 2012 Figure 4. Evidence of well beyond what happens under stand- 1DRHCT@KRSGNQCDQjS the CCD stitching 1DRHCT@KRSGNQCDQjS CHRBNMSHMTHSHDR ard operating conditions. pattern as revealed by #HEEDQDMBD3G Ql+%"B@KHAQ@SHNM

B the LFC wavelength R U

l calibration. Due to the When looking at sequences of data dur- L

D paucity of spectral lines,

U ing which we did not intervene to modify D U TQ the Th-Ar calibration the system (orange and violet vertical TQ B was unable to identify B this effect. From Wilken stripes in Figure 5), the stability was seen et al., 2010. to be superb. As in almost all series, the KHAQ@SHNM @ KHAQ@SHNM

@ RMS of the relative drift between the two

RNEB l l channels is consistent with the photon RNEB noise of ~ 7 cm/s. In order to decrease l l the contribution of the photon noise, we 1DRHCT@K

1DRHCT@K added an increasing number of expo- l l sures and computed the Allan (or two- sample) deviation (Figure 6). This estima- l l tor is capable of distinguishing statistical ""#OHWDKHMMCDBGDKKDNQCDQ noise processes from systematics, e.g., drifts. In Figure 6 we see that the orange and violet points, corresponding to two ~ 34 cm/s over the whole run. When the 5 cm, was used to couple the LFC outgo- quiet LFC series, follow well the curve CCD cooling was stopped, and then ing fibre to the HARPS calibration fibres. of the estimated (not fitted) photon noise, restarted, we could measure a drift of We do not yet understand the cause of up to a level of ~ 2.5 cm/s, where the 13 m/s on the individual channels, but this drift, but speculate it could be related data flatten. At this point systematics limit the relative drift between channels was to the strong intensity variation (close the stability of the system. Short-term below 40 cm/s peak to valley, an indi to two orders of magnitude) or to a differ- (~ 2 hours) repeatability of the LFC+ cation that the method of simultaneous ent occupation of the modes after the HARPS system is at the level of 2.5 cm/s. reference in HARPS is capable of reduc- transition through the integrating sphere. Although we cannot say the same for ing systematic effects by more than a Possible alternative explanations point the long-term stability due to the various factor of 30, at least when they originate towards detector effects that could dis- drifts exemplified in Figure 5, we stress from the detectors. tort the instrument profile depending on once more that these instabilities in the light intensity, or data reduction effects, long term were most likely generated Two large deviations in the relative drift also related to a change of the instrument from our interventions in the system. In between the two channels are seen in profile for very faint signals. Work is still Figure 6 we display a similar measure- the data (Figure 5). These correspond being done to understand these measurement for Th-Ar calibration, and the limita- to the series of spectra acquired when ments, but it must be stressed that this is tion of Th-Ar lamps with respect to the an integrating sphere, with a diameter of LFC is clearly visible.

November 2010 January 2011 8 Channel A Series 1 Series 2 Channel B A–B 6 Figure 5. Drift of the two spectrograph channels for all the LFC 4 data collected between November 2010 and

ence (m/s) January 2011 (almost

fer 1300 spectra) is shown. 2 The drift of the individual channels is measured with respect to an arbi- 0 trarily chosen spectrum. The relative drift between them is shown in black. The orange

Computed velocity dif –2 and violet vertical stripes indicate two long Integrating sphere CCD cooling off series (> 200 spectra in total) during which –4 time the system was left unperturbed. From 0 200 400 600 800 1000 1200 Wilken et al., 2012.

The Messenger 149 – September 2012 5 Telescopes and Instrumentation Lo Curto G. et al., Spectrograph Calibration at the Exo-Earth Detection Limit

During our test runs in La Silla we moni- 25 Figure 6. Two-sample tored the radial velocity variation of the variance of the LFC and the Th-Ar calibration. solar-type star HD 75289, known to host The black solid line is an a Jupiter-mass planet with a period of estimation of the photon 10 3.5 days. Using the LFC for wavelength noise. The dashed hori- calibration and simultaneous reference, zontal lines at 10 cm/s and 2.5 cm/s indicate, we could reconstruct the orbit of the exo- for the Th-Ar and the planet. The measurements calibrated LFC simultaneously, the with the LFC nicely agree with previous level at which the data data and the deviations from the fit could 2.5 no longer follow the estimated noise and sys- be due to stellar activity or pulsations. tematic effects become To our knowledge this is the first time that LFC series 1 important. From Wilken the orbit of an exoplanet has been recon- 2-sample deviation (cm/s) LFC series 2 et al., 2012. structed using LFC calibrations. 1 Thorium lamp Photon noise

During the four years of the programme 0.5 the LFC system has improved much, 108 109 1010 1011 not only in its performance, but also in Accumulated photons robustness and operational stability. The laboratory test and the campaigns with refine the observation strategy for and the E-ELT. The experience collected HARPS have achieved successful results, ESPRESSO planet searches. with the HARPS LFC will be invaluable for which have consolidated the concept of ESPRESSO and beyond. the system. The achieved repeatability of The radial velocity (RV) precision of 2.5 cm/s is sufficient to detect an Earth- HARPS is estimated to be around While delivering top RV precision data like planet in a one-year orbit around a 60 cm/s (Lovis et al. 2006). Knowledge of with HARPS, this project would permit an star like our Sun. the instrument has permitted the instru- understanding of the long-term system mental causes that limit the RV precision atics (if any), early optimisation of comb to be identified: the light injection system operations and of the reduction software Laser frequency comb for HARPS and scrambling, the wavelength calibra- before ESPRESSO goes online and well tion system and, to a lesser extent, the in advance of the preliminary design of After the successful completion of the temperature variations of the detector. any high resolution spectrograph for the demonstrator programme, beginning in After commissioning a new injection sys- E-ELT. February 2012, in partnership with the tem in 2009, which improved the image Instituto de Astrofisica de Canarias and stability at the fibre entrance, the Th-Ar the Universidade Federal do Rio Grande wavelength calibration system is the Acknowledgements de Norte, we started a project aimed at strongest limiting factor to the long-term We wish to thank Gerado Avila from ESO for prepar- the acquisition of a turn-key LFC system RV precision of HARPS. With the LFC, ing the injection and the scrambling unit, for HARPS. The system will be offered which has been shown to have a stability and Francesco Pepe, Christophe Lovis and Bruno to the astronomical community after suc- as good as a few cm/s with HARPS, the Chazelas from the Geneva Observatory for their help cessful commissioning at the telescope. instrument is capable of reaching long- with the reduction software and their advice. This project is not only directed towards term RV precision below 30 cm/s, giving improvement of HARPS, but also towards access to the detection of Earth-mass References future instruments like ESPRESSO. The planets in close-in orbits, tracing out goals of this programme are to: the path towards the detection of Earth Araujo-Hauck, C. et al. 2007, The Messenger, 129, 24 – gain experience in the use of the LFC, twins. This RV precision is midway be- Beringer, J. et al. 2012, Phys. Rev., D86, 010001 study its long-term behaviour and its tween the current HARPS performance Liske, J. et al. 2008, MNRAS, 386, 1192 reliability in operations, optimise the and the 10 cm/s precision expected for Lo Curto, G. et al. 2010, Proc. SPIE, 7735, 77350Z reduction tools to achieve the best per- ESPRESSO at the VLT, planned to start Lovis, C. et al. 2006, Nature, 441, 305 Mayor, M. et al. 2003, The Messenger, 114, 20 formance with the LFC, with a view operations in about four years. The LFC Murphy, M. et al. 2007, MNRAS, 380, 839 to its use on VLT and E-ELT instrumen- calibration system will be one of the key Palmer, B. & Engleman, R. 1983, Atlas of the tation; components of ESPRESSO. Thorium spectrum, Los Alamos National – bridge the gap between HARPS and Laboratory Steinmetz, T. et al. 2008, Science, 321, 1335 ESPRESSO and acquire the potential of The step of moving from a laboratory Wilken, T. et al. 2010, Proc. SPIE, 7735, 77350T detecting a population of super-Earths prototype to a device to be operated at Wilken, T. et al. 2010, MNRAS, 405, L16 in the habitable zone of solar-type stars; the telescope on an existing instrument Wilken, T. et al. 2012, Nature, 485, 611W – improve HARPS precision, which in will move us to the production phase, turn will improve our capability for find- and will drive the development of an op ing low-mass planets, further the erational comb for the next high-precision understanding of stellar activity and radial velocity instruments for the VLT

6 The Messenger 149 – September 2012 Telescopes and Instrumentation

ESO VISTA Public Surveys — A Status Overview

1 500 Figure 1. Overview of Magda Arnaboldi P85+ Marina Rejkuba1 the VISTA time alloca- 1 400 tion in hours. P85+ Jörg Retzlaff P86 included dry runs which 1 Nausicaa Delmotte 300 were executed before Reinhard Hanuschik1 P87 the official start of VISTA Michael Hilker 1 200 operations. 1 P88 Wolfgang Hümmel 100 Gaitee Hussain1 Valentin Ivanov 1 0 P89 Alberto Micol1 e VV V VH S 1 VM C VIDE O

Mark Neeser VIKING 1 Monika Petr-Gotzens Open tim Ultra-VISTA Thomas Szeifert 1 Fernando Comeron 1 six VISTA PSs from the extended period imager VIRCAM is provided by Emerson Francesca Primas 1 85 to period 89 (P85–P89). et al. (2006). Observation preparation Martino Romaniello 1 and submission for public surveys is The implementation of the PSP recom- done on a half-yearly basis, following the mendation on time to survey completion standard ESO service mode procedures. 1 ESO implied a revision of the standard VLT The PIs of VISTA public surveys and their model of scheduling observing time in teams submit Observation Blocks (OBs) service mode because the VISTA public — the standard basic observing units. The ESO policies for public surveys survey programmes are all essentially The deeper surveys (Ultra-VISTA, VIDEO, include regular monitoring and reviews at the highest priority of execution. As an VIKING and VMC) have typically ~ 1-hour- of the progress of the surveys to en- added complexity, normal programmes long OBs, while the wide surveys (VHS sure their legacy value and scientific were scheduled alongside public surveys and VVV) have OBs lasting between 5 competitiveness. The review process is and Chilean programmes from P87. and 30 minutes. The survey with the larg- carried out on the basis of reports by Because the former have top priority and est number of submitted OBs is VVV: the ESO survey team and the survey PIs essentially cover all observing condi- because of the multi-epoch observations submitted to the relevant Public Survey tions, normal (open time) programmes the total number of OBs prepared and Panel (PSP) — the VISTA PSP in this must also be assigned a similar priority if executed will be of order 30 000. Figure 2 case. A summary of the time allocation they are to be executed at the telescope. shows the number of hours of execution to VISTA surveys, the service mode Starting from P88, normal programme of OBs each month for all VISTA surveys. observations and the current progress observations are not carried over regard- The time charged for each OB execution after two years of telescope operation less of their ranking, to avoid extra carry is only counted for successfully com- is provided. Furthermore the content overs hindering the progress of the pleted observations and Figure 2 shows of the data products delivery by the surveys. To limit the impact of open pro- the completed OB hours that are com- survey teams to the ESO Science grammes on the progress of the VISTA puted by the observation preparation Archive Facility is described. PS the following policy has been imple- software (P2PP3). While in the first year mented since P89: open time proposals of the operations there was still some can access restricted right ascension fine-tuning of the operational procedures Phase 1 — time allocation to surveys ranges, but should carefully justify the and overheads, now the overheads com- scientific goals and why these scientific puted by version 3 of the Phase 2 Pro- Scheduling of the VISTA Public Surveys goals are not achievable through the posal Preparation system (P2PP3) are (PS) is done in line with the VISTA PSP scheduled PS. very similar to the actual time needed to recommendation that every effort should execute the observations. be made to complete the surveys within five years. Realistic expectations on what Phase 2 — service mode observations The histogram in Figure 2 shows the can be executed in the next semester for public surveys effect of technical interventions on are also taken into account, based on the speed of execution of the public sur- experience gained from the previous VISTA public surveys are ambitious vey OBs, with the main impact falling semester(s) of VISTA operation. The time programmes which entail very large allo- in the period 3 April 2011 to 4 May 2011, allocation to surveys is based on the cations of time, of order of 1800 to which coincided with the recoating of updated observing request by the PS 3400 hours, with consistent observing the primary (M1) and secondary (M2) mir- principal investigators (PIs) and takes into conditions. For a summary of the scien- rors with aluminium due to fast degra account the carryover time needed to tific goals of the VISTA public surveys, dation of the original silver coating, and complete the observations submitted in their area coverage and photometric an extended recovery and maintenance the previous period. Figure 1 provides characteristics, see Arnaboldi et al. (2007). of M1. an overview of the time allocation to the An overview of VISTA and of its wide-field

The Messenger 149 – September 2012 7 Telescopes and Instrumentation Arnaboldi M. et al., ESO VISTA Public Surveys — A Status Overview

250.0 Figure 2. Histogram of VISTA public survey completion rates the number of hours of execution of OBs each month for all VISTA sur- Here we present the current fraction of 200.0 veys up to 1 April 2012. completeness for each VISTA PS and the

r) Quality control grade A expected time to completion, based on

(h is assigned to OBs com- the current efficiency of execution. The 150.0 pleted fully within ion requested constraints absolute completion rate is based on the- (i.e. sky transparency, oretical OB execution times as computed ecut 100.0 image quality, airmass, by the P2PP execution time module and ex Moon illumination, etc.), the time requested by the PI of each sur-

OB while grade B is assigned to those OBs vey for the total duration of the project, 50.0 for which one of the as described in the Survey Management constraints is violated Plan (SMP). The absolute completeness up to ~ 10%. fraction is given by the ratio of the com- 0.0 pleted OB time divided by the time re 11 11 11 11 11 11 12 12 10 10 10 10 10 10 09 r- r- v- y- r- quested in the SMPs. The completion y- v- v-

Jul- Grade A Jul- Jan- Ma No Sep- Jan- Jan- Ma Ma

Ma rates are calculated for the observations No Sep- Ma No Grade B up to the end of Period 88 (end of March In order to enable the survey teams to area definition file generated with SADT. 2012), hence they cover the first four prepare large numbers of similar OBs In this way hundreds of similar OBs periods of VISTA operations. In these four and for ESO user support and science that adopt the same observing strategy periods, the effective telescope time operations to verify and execute them and point to different areas in the sky is about 1.75 years, as there were three in the most efficient manner, new tools are generated automatically, thus pre- months of technical downtime (mirror have been developed (Arnaboldi et al., venting typing errors and saving time. In coating, M1 intervention and technical 2008). We list them briefly: addition to an interface with the SADT, downtime to correct the focal plane tilt). this tool also allows the survey PIs to These technical interventions affected The Survey Area Definition Tool (SADT) define the survey observing strategy via mostly the VVV and Ultra-VISTA projects, was developed by the VISTA consortium scheduling containers. These concepts as they took place in those months (led by J. Emerson) and delivered as can be easily encoded in an automatic when either the Milky Way Bulge or the part of the United Kingdom in-kind con- ranking algorithm that suggests to the COSMOS fields are visible. tribution to joining ESO. The main role observers which OB is to be selected out of the SADT is to efficiently mosaic the of many thousands of similar survey OBs. The absolute completion rates of the survey area and to identify the necessary The OT is used on Paranal for selecting surveys at the end of P88 are listed in active optics and guide stars for each the observations to be executed; it has Table 1. These can be used to extrapo- tile. The SADT has been further improved the VISTA-specific ranking algorithm late the time necessary to complete following the experience gained during (Bierwirth et al., 2010) as well as report- the VISTA public surveys, assuming that VISTA science verification, dry runs, and ing functionality. the observations continue at a similar the first period of observations (P85+). pace. From these assumptions, the VHS The latest improvement was to introduce Survey Monitoring and Visualisation survey can be completed in about five the 2MASS catalogue transformation Tool (SVMT) is a new tool developed to years, while VVV, Ultra-VISTA, VIDEO and to I-band magnitudes, which is now used facilitate the Phase 2 review of thousands VMC are all expected to take more than for guiding and active optics on VISTA. of survey OBs and to enable monitoring seven years. These numbers are lower This is important, as it was noticed that of the survey observations. The main limits as the requested observing time in other catalogues suffered from low reso- functionalities are the display of the sur- the SMPs was computed using overhead lution, containing binary stars or galax- vey areas and the OB status for selected values that later proved to be underesti- ies, and some defects (e.g., containing areas or survey runs, and the visualisa- mates. As the survey projects progress, spurious sources due to scratches on tion of the distribution on-sky for the sub- and once one of the approved surveys is the plates from which these surveys were mitted survey data products. Basic completed, the speed of completion is derived) which caused execution time statistical functionalities have been imple expected to increase for the other sur- losses due to the choice of unsuitable mented, such as calculation of the surveys. The VIKING survey was set to the guide and/or active optics stars. vey area and accumulated exposure lowest priority in P89 (October 2011– times for which the observations have March 2012), as this survey currently fails Phase 2 preparation tool for surveys been completed or the data products to comply with the Phase 3 policies of (P2PP3) and Observing Tool (OT) for submitted. This tool is used by the User data products submission for the ESO public survey support have resulted from Support Department and Archive Sci- public surveys. Additional time allocation the evolution of the main ESO observa- ence Group, for the purpose of Phase 2 for the public surveys is pending the tion preparation and execution tools. The and Phase 3 reviews, respectively, and completed delivery of the agreed data PS teams prepare the observations using for overall survey progress monitoring by products. P2PP3 which takes as input the survey the ESO Survey Team (EST).

8 The Messenger 149 – September 2012 Table 1. Overview of the absolute completeness of the VISTA public surveys after 1.75 years of are condensed into a few terabytes of VISTA observing time (effective). data products each year. Because of the legacy value of the public survey data Period VVV VMC VIKING Ultra-VISTA VIDEO VHS products, ESO’s policy is to ensure their 01.04.2010–30.03.2012 24 % 22% 32% 29% 25% 38% long-term archival storage and public accessibility in order to promote their wide scientific use by the astronomical VISTA science operations Catalogue 2 (GSC2) optical catalogue community at large, beyond those scien- with the 2MASS near-infrared catalogue, tific goals initially identified by the sur- The VISTA telescope and its near-infrared and by extending the latter catalogue to vey teams. In order to bring this about, camera VIRCAM are in normal operation: include synthetic optical magnitudes. ESO has set in place a whole new pro- science data are being taken, and deliv- The high elongation of the measured point cess, called Phase 3, which represents ered to the users. Currently, the typical spread function (PSF) detected during the final step in the execution of ESO technical downtime is 2–3%, to be com- early telescope operations is now mostly large programmes and public surveys. pared with 10–12% of weather down- under control and resolved. Occasionally time. During the commissioning of VISTA elliptical images are recorded, typically The new Phase 3 infrastructure was and VIRCAM, the overheads for telescope due to azimuth axis oscillations that deployed on 10 March 2011; it supports pointing, guiding and camera setup appear at seldom and irregular intervals. the reception, validation and publication turned out to be ~ 30% larger than the of data products from the public survey overheads estimated by the VISTA con- Several optimisation steps were intro- projects and large programmes to the sortium. Several actions were then imple- duced into the instrument and telescope ESO Science Archive Facility; for a mented to reduce the various sources operation to increase the efficiency of description of the Phase 3 tools and the of overhead. Furthermore, the telescope observations: relaxing the declination tol- infrastructure see Arnaboldi et al. (2011). efficiency is about 10% lower than ex erance of the AO correction and par Data products must be consistent pected because the original silver mirror allelising the instrument and telescope with the data standards documented by coating was replaced with aluminium setups to decrease the overheads. Finally, the Archive Science Group at ESO. in April 2011, due to the fast degradation the calibration plan was further revised, These data standards are required to of the earlier coating. In Table 2 we pro- giving an extra 40 minutes per night for characterise the level of data reduction vide the zero-point measurements in survey OB execution. Further hardware and calibration, to track provenance, early operations with silver coating (dat- improvements are not realistic; software which allows ESO to monitor survey pro- ing from October 2009), the last meas- developments and further improvement gress, and finally to support the query urements for silver (from March 2010) and of operations procedures may effectively for specific data products via the ESO the zero point with the new aluminium improve progress speed, but only by a archive interfaces. In the context of the coating (measurements from July 2011). few percent. Phase 3 process, the data products returned by the survey teams are regu- The ESO policies for public surveys larly monitored with respect to the actu- Table 2. Photometric zero-point measurements entail that raw data become public as ally executed observations. The timeline (Vega magnitudes) in early operations (October soon as they are ingested in the ESO defining the requested delivery dates 2009) with silver coating, last silver coating values (taken March 2010) and with the new aluminium Science Archive Facility (SAF). Following by type of data product is given by the coating (July 2011). the Memorandum of Understanding Phase 3 policies. for VISTA, the Cambridge Survey Unit Filter October March July (CASU) receives a copy of all the raw For the VISTA data, a number of prod- 2009 2010 2011 data collected by VISTA for public sur- uct types have been identified: images, Ks 23.03 22.88 22.96 veys and normal programmes. PIs of weight maps and source lists. As high- H 23.87 23.61 23.76 VISTA public surveys do not automatically level data products, the resulting source J 23.78 23.43 23.66 receive a copy of the raw data, but can catalogues from the PS projects repre- Y 23.45 22.97 23.33 access the pipeline data products either sent particularly important resources. Z 23.82 23.22 23.58 from CASU or the Wide Field Astronomy The catalogues are different from the Unit (WFAU) archive in Edinburgh. Raw source lists, which are per-tile products data are delivered regularly upon request and can be downloaded as entire FITS During current standard operations, typi- to the Ultra-VISTA team. tables. The catalogue contents will cal VIRCAM/VISTA technical downtime be searchable via a dedicated query is due either to the M2 unit or active interface in the ESO SAF, which should optics (AO) and autoguiding (AG) related Phase 3 – data products from public sur- become available in the second half problems. The AO and AG problems are veys of 2012. Basic functionalities will be sup- partially caused by the incompleteness ported to allow the archive user to carry of the catalogues used by SADT to select The raw data collected at the survey tele- out searches by position as well as guiding stars. The catalogue issue was scopes for the different projects amounts by non-positional source parameters for improved by replacing the Guide Star to about 1.5 TB per month, which, in turn, sources in any area of the sky visible

The Messenger 149 – September 2012 9 Telescopes and Instrumentation Arnaboldi M. et al., ESO VISTA Public Surveys — A Status Overview

Table 3. Overview of the ESO Phase 3 data releases resulting from the VISTA public surveys.

Survey Submission Date of Release Content Filter Sky Type of Data Total Total Publication Date Observations Coverage Products Volume Number Date (sq.deg) of Files VVV 03.05.2011 Feb 2010–Sep 2010 Contiguous patch of ZYJHKs ~ 520 Tiles 1.5 TB 7980 25.07.2011 Bulge and Disc region (348 tiles) Single-band source lists including multi-epoch data in Ks

VIDEO 03.05.2011 Nov 2009–Feb 2010 XMM-LSS field YJHKs 1.5 Tiles 24 GB 291 25.07.2011 Single-band source lists

VMC 08.09. 2011 Nov 2009–Nov 2010 Two tiles in the LMC: YJKs 3 Stacked tiles and 8.1 GB 1256 25.09.2011 one overlapping 30 pawprints Doradus and the other Single-band and band- the South Ecliptic Pole merged source lists region

VHS 15.09.2011 Nov 2009–Sep 2010 VHS DES – YJHKs ~ 19 10 Tiles 3.9 TB 96474 17.10.2011 120 s in JHK Pawprints VHS ATLAS – Single-band source lists 60 s in YJHK VHS GPS – 60 s in JK

Ultra- 06.10.2011– Dec 2009–Apr 2010 Deep imaging of the YJHKs, 1.5 Stacked images, 87 GB 19 15.02.2012 VISTA 30.01.2012 COSMOS field NB118 SExtractor catalogues including w-selected multi-band catalogue

VIKING 10.10.2011 Phase 3 data submission to be closed by PI – – 19 GB 6276 –

from the La Silla Paranal Observatory, for further scientific selection and investigation on the user’s computer.

Table 3 provides an overview of the ESO Phase 3 data releases resulting from the VISTA public surveys and Figure 3 shows a map with the sky coverage. A detailed description of the data releases is available1. These release pages are based on the information provided by the PIs and give an overview of the obser vations, a description of the data reduction and calibration, additional release notes illustrating the scientific quality of the data and any additional useful information regarding the content of the release. The data products from each VISTA public survey are available via the query form2 or by following the link at the bottom of each release description page.

Figure 3. The VISTA public survey data products released through the Phase 3 process in 2011/2012 cover almost 2500 square degrees of the southern hemisphere. Colour coding: VHS–green, VVV–red, VMC–yellow, VIDEO–pink, UltraVISTA–purple. Entire survey footprints are shown in light blue.

10 The Messenger 149 – September 2012 The first public data release from the actively carrying out their observations References VISTA public surveys took place in and achieving their scientific goals: as Arnaboldi, M. et al. 2011, The Messenger, 144, 17 December 2011. Since then, more than documented by the nine ESO press re Arnaboldi, M. et al. 2008, The Messenger, 134, 42 five thousand files and 2.0 TB of VISTA leases based on VISTA data since Janu- Arnaboldi, M. et al. 2007, The Messenger, 127, 28 data products have been downloaded ary 2010 and the 23 refereed papers from Bierwirth, T. et al. 2010, SPIE, 7737, 19 from the ESO SAF by the community. The ESO public surveys thus far. In order to Emerson, J., McPherson, A. & Sutherland, W. 2006, The Messenger, 126, 41 most requested and downloaded data increase community awareness of the product type is the source list (in FITS scientific research opportunities from the table format). VISTA public surveys, ESO is organising Links a workshop on 15–18 October 2012 enti- 1 Description of the Phase 3 data release: tled “Science from the next generation http://www.eso.org/sci/observing/phase3/data_ 3 Conclusions imaging and spectroscopic surveys” . releases.html The astronomical community is invited to 2 Query form for data products from each VISTA VISTA survey operations have now access the opportunities provided by the public survey: http://archive.eso.org/wdb/wdb/adp/ phase3_vircam/form reached a steady state and nearly 80% large wealth of data products delivered 3 Homepage of the workshop “Science from the next of the night-time on VISTA is used to by the public surveys and to use them to generation imaging and spectroscopic surveys”: successfully execute survey observa- explore science goals beyond those origi- http://www.eso.org/sci/meetings/2012/sur- tions. The VISTA public survey teams are nally identified by the VISTA PS teams. veys2012.html ESO/INAF-VST

This large field colour image of the nearby edge-on spiral galaxy NGC 253 was composed from VLT Survey Telescope (VST) images in g-, r- and i-bands. NGC 253 is a member of the Sculptor group at a distance of about 3.5 Mpc and as the nearest starburst galaxy shows signs of disc disruption and outflowing ionised gas. The dust absorption, well seen in this image, obscures the central starburst and possibly an active galactic nucleus. More details are available in Release eso1152.

The Messenger 149 – September 2012 11 Telescopes and Instrumentation

On the Photometric Calibration of FORS2 and the Sloan Digital Sky Survey

Daniel Bramich1 lute calibration is substantially more chal- in order to identify the minimum require- Sabine Moehler 1 lenging to achieve than a precise relative ments for a certain photometric preci- Lodovico Coccato1 calibration due to the inherent difficulties sion. To each simulation realisation, we Wolfram Freudling1 in minimising the systematic uncertainties fitted a photometric model that analyses Cesar Enrique Garcia-Dabó1 between the spectral energy distribution a large number of nights of data simul Palle Møller1 of appropriate (and usually very bright) taneously. For this purpose, we devel- Ivo Saviane1 photometric standards and the natural oped a general IDL program1 to perform photometric system of the observations. photometric modelling, including both absolute and relative photometric calibra- 1 ESO tions. This software allows the user to FORS2 photometry fit any linear photometric model (i.e. any sum of photometric terms) to a set of An accurate absolute calibration of With the Very Large Telescope (VLT) magnitude measurements. The main photometric data to place them on a FORS2 instrument, we aim to provide the results from our modelling of the simu- standard magnitude scale is very user with the possibility, given sufficient lated data are the following: important for many science goals. science target signal-to-noise (S/N), of 1) To achieve ~ 1% precision for the pho- Absolute calibration requires the obser- performing an absolute calibration of their tometric zero-point, two standard star vation of photometric standard stars photometry to an accuracy of better images per night should be obtained and analysis of the observations with an than 3% on photometrically stable nights. at airmasses of ~ 1.1 and 1.8, ensuring appropriate photometric model includ- This is a challenging problem both in a range in airmass of ~ 0.6–0.7, and ing all relevant effects. In the FORS terms of collecting appropriate standard at least 18 photometric nights should Absolute Photometry (FAP) project, we star observations as well as with regards be included in the photometric model have developed a standard star observ- to modelling the standard star photometry. to be fitted. This result is based on ing strategy and modelling procedure the assumption that the extinction that enables calibration of science tar- The photometric model should not only coefficient is stable for the time period get photometry to better than 3% accu- account for a photometric zero-point, over which the standard star images racy on photometrically stable nights nightly extinction coefficients and colour are observed on any one night. given sufficient signal-to-noise. In the terms to convert from the standard filter 2) Observations coupled with modelling application of this photometric model- wavebands to the instrumental wave- that satisfies the constraints described ling to large photometric databases, bands, but should also potentially include above should enable the atmospheric we have investigated the Sloan Digital terms to model the static and rotating extinction coefficient to be determined Sky Survey (SDSS) and found system- residual flatfield patterns (Freudling et al., to a precision of ~ 6–8%. atic trends in the published photometric 2007; Moehler et al., 2010). The latter 3) The FAP project goal, to allow the data. The amplitudes of these trends effect was found to be caused by the lin- user to reach an absolute photometric are similar to the reported typical preci- ear atmospheric dispersion compensator accuracy of 3% during photometric sion (~ 1% and ~ 2%) of the SDSS (LADC) and was worst for the LADC nights, may be achieved by following photometry in the griz- and u-bands, used with the now retired FORS1 instru- the constraints described above, which respectively. ment. The LADC used with FORS2, how- lead to the ability to reach absolute ever, shows mainly a gradient (of ampli- photometric accuracies of 1.4–1.8% tude 1.5% peak-to-valley) instead of a (given sufficient science target S/N). The general photometric calibration complicated pattern. The necessity for a 4) Once two standard star images at air- problem photometric model to account for all masses of ~ 1.1 and 1.8 have been these effects leads to requirements for obtained, further images at intermedi- Calibration of science target photometry non-trivial modelling software. Further- ate airmasses have little impact on consists of fitting an appropriate photo- more, the standard star observations the precision of the monitoring of the metric model (e.g., zero-point, extinction need to be designed to provide plenty of photometric zero-point and the extinc- and colour coefficients, etc.) to the cali- photometric measurements over suffi- tion coefficient for the night in ques- bration data (standard star observations) cient ranges in airmass, time, colour, tion, but will be needed to monitor the and then using the photometric model spatial coordinates and rotator angles photometric stability of the night. parameters to derive the photometric during photometrically stable nights. corrections that should be applied to the Comparing the requirements defined by science observations. Sometimes it is these simulations to the calibration plan convenient to split the calibration problem Simulated FORS2 observations we found that: into an absolute calibration (i.e. knowl- a) The standard star fields for each month edge of fluxes in physical units such as To understand how to provide calibra- did not provide calibrating stars with J m–2 s–1) and a relative calibration (where tions that allow better than 3% absolute a sufficiently wide and homogeneous all observations are calibrated to the photometric accuracy with FORS2, we range of colours. same instrumental flux scale). This split- performed extensive simulations and b) The calibration plan needs to include ting is necessary since an accurate abso- modelling of standard star observations standard star observations at both

12 The Messenger 149 – September 2012 high and low airmass to allow a correct new calibration plan is now followed in 2) Up until December 2011, the Septem- judgement of the photometric quality about 75% of the nights where it is appli- ber 2007 version of the Stetson cata- at the start of the night (as opposed to cable (i.e. potentially photometric nights). logue of standard stars was used an observation of just one standard Most of the potentially photometric nights by the FORS2 pipeline. A newer ver- star field near zenith). during which it is not fully followed are sion is available (December 2010 3) c) In order to judge the photometric qual- nights in which FORS2 is used for only which contains BVRI photometry of a ity based on a single observation, part of the night. larger number of stars in fields that the extinction derived assuming a well- are part of the calibration plan and determined instrumental zero-point increases the coverage in very sparse should be used, as opposed to deriv- Fit of photometric model for FORS2 fields by up to a factor of three. Hence ing a zero-point from an average we adopted this newer standard star extinction (which shows a correlation With the new calibration plan in place, catalogue. with airmass if the true extinction dif- a sufficiently large dataset is routinely col- 3) The FORS2 pipeline recipe fors_ fers from the average extinction). lected to fit our photometric model. zeropoint uses SExtractor (Bertin & The FORS2 pipeline provides two recipes Arnouts, 1996) to perform the back- for that purpose, called fors_zeropoint ground subtraction and measure the New calibration plan and fors_photometry. The former iden standard star flux. The settings used tifies standard stars with catalogued as default values were optimised for Triggered by these findings, we changed magnitudes in each frame, and performs the Landolt catalogue (Landolt, 1992) the FORS2 imaging calibration plan. At aperture photometry. The latter fits our that was originally used and which the beginning of every night without visi- model to the data of several nights, and contains a few bright, isolated stars, ble clouds, one standard star field near computes, in addition to a number of whose catalogued magnitudes were zenith is observed. If the extinction nuisance parameters (viz. model parame- measured with classical aperture coefficient derived from this observation ters which need fitting but whose values photometry. The detection threshold (using the latest best estimate of the we are not interested in, which in this in fors_zeropoint was therefore set zero-point) is consistent with the extinc- case are the true instrumental object rather high and a global background tion coefficient limits for a photometric magnitudes), a single zero-point for these subtraction was used. The aperture night, then a second standard star field at nights and an extinction coefficient for size was set to 14 arcseconds in dia high airmass is observed immediately each night. meter, corresponding to the aperture afterwards to verify the stability of the used by Landolt. extinction coefficient. If both observations To obtain reliable results, several im The Stetson catalogue, on the other yield the same extinction coefficient, then provements had to be made to the reci- hand, reports magnitudes derived the night is declared to be photometric. pes, the parameters to run those recipes, using adaptive aperture photometry, If science data requiring photometric and the data distributed with the reci- i.e. the aperture size increases until it conditions are observed in service mode, pes2. Specifically, the following changes encounters the next star. In addition, then additional standard stars have to were made: many of the Stetson fields are quite be taken at the middle and at the end of 1) We found that the automatic identifica- densely populated, so that a global the night to allow monitoring of the pho- tion of standard stars by the FORS2 approximation of the background is tometric stability of the night. pipeline recipe fors_zeropoint was not problematic. The higher star density robust, sometimes resulting in mis- also makes it advisable to lower the The standard star fields are observed identifications that can cause incorrect detection threshold to enable SExtrac- with offsets in position and rotation extinction coefficients to be derived. tor to also correct for stars detected angle to allow the presence of static and We replaced the original pattern- inside the aperture. We therefore low- rotating residual flatfield patterns to be matching algorithm used in this recipe ered the detection threshold in fors_ investigated. After problems experienced with a robust algorithm that identifies zeropoint from 3 σ to 1.5 σ and with some of the Stetson standard star the shift between the standard stars decreased the aperture size to 10 arc- fields (Stetson, 2000) due to a lack of in the catalogue and the detected seconds in diameter. In addition we stars, we carefully selected a new set of objects in the image by building up a switched from global to local back- Stetson fields that primarily satisfy the histogram of all possible shifts between ground fitting. These changes reduced airmass constraints in the new calibration the standard stars and the detected the scatter in the derived photometric plan, and that are further optimised objects and finding the histogram peak zero-points from individual stars within for the number of standard stars that are (which is very pronounced for ≥ 4 one image by more than a factor of observed along with the colour range standard stars in the field). Although two on average. that is achieved. this algorithm can only cope with very small rotations (≤ 0.3 deg), this is not We experimented with the number of The new FORS2 calibration plan (includ- a problem because rotations in the nights needed to obtain reliable fits of our ing the new standard star fields) was put FORS2 world coordinate system (WCS) model. We found that a minimum of into operation on 24 October 2011, and are extremely rare. seven fully photometric nights were compliance was carefully monitored. The needed. We therefore adopted the follow-

The Messenger 149 – September 2012 13 Telescopes and Instrumentation Bramich D. et al., Photometric Calibration of FORS2 and the Sloan Digital Sky Survey

ing procedure to collect the data for each model fit. For each night, we chose a range of dates that is large enough to include at least seven fully photometric nights around that night. During periods with few fully photometric nights, this means that a date range of up to 60 nights needed to be included in the analysis. The number of seven photometric nights is a compromise between the increase in accuracy with an increasing number of photometric nights and tem- N ONHMS Q

poral resolution of the parameters. In Fig- YD ure 1 we show a comparison between the results of a fit that used a fixed window of 28 nights, not including the above pipeline improvements, and a fit using the current procedure. It can be seen that the zero-points change by less than about 5% over a range of 100 nights.

We believe that the photometric parameters obtained with the procedure as outlined above are accurate enough to ,)# photometrically calibrate science data if a night is photometric. However, the user Figure 1. Three estimates of nightly photometric The two detectors in FORS2 are distinguished by should be aware that the new calibration zero-points for FORS2 over 100 nights. The black open and filled points. It can be seen that by fitting a points are computed using averaged extinctions as photometric model, zero-points can be obtained plan is not sufficient in itself for establish- done for quality control. The red points are com- with an accuracy of a few percent. The fairly stable ing that a night is photometric. There is a puted using our photometric model but without the difference in zero-point between the two chips is finite risk that a non-photometric night improvements to the pipeline as described in the clearly visible. has not been recognised as such by the text. The blue points are our best current estimates. classification performed at Paranal. It is therefore advisable, that for science ob- The large size of the SDSS survey makes our methodology to investigate any sys- servations requiring photometric condi- it challenging to search for biases. Since tematic trends that might still be present tions, the user requests further standard our software is capable of handling such in the SDSS photometric data after the star observations during the night. A pro- a large dataset, we decided to use it for Padmanabhan calibration effort. To this cedure to submit standard star observing an investigation of the SDSS photometry. end, we downloaded all of the SDSS blocks without having to specify which photometric data down to 19 mag in standard star field is to be observed is The SDSS (York et al., 2000) provides each waveband and analysed the repeat currently under preparation. Another tool photometry (including widely used aper- observations that satisfy certain quality to judge the quality of a given night is ture and point spread function [PSF] constraints. We considered the aperture the MeteoMonitor tool 4. This tool should magnitudes) in the ugriz-bands for (7.43 arcseconds) and PSF magnitude be consulted if the data of any given night objects down to ~ 22.5 mag and covering measurements, and we looked for trends are to be used for photometry. ~ 14555 square degrees. Padmanabhan as a function of image and observation et al. (2008) developed a photometric properties, such as detector column and calibration model for SDSS data, similar row, PSF full width at half maximum SDSS photometry to the model that we developed for (FWHM), sub-pixel coordinates, etc. FORS2, but with many more (~ 2000) cal- Our modelling of historical FORS2 photo- ibration parameters of interest and ~ 107 In the upper panel of Figure 2, we show metric data revealed subtle effects, such nuisance parameters to be solved for, how measured u-band aperture magni- as a rotating illumination pattern that that results in a relative photometric cali- tudes systematically change as a func- can be corrected to improve the photo- bration that is good to ~ 1% in the griz- tion of PSF FWHM for a single detector in metric accuracy. This raises the question bands (~ 2% in the u-band). the SDSS camera, and we note that the of whether other large photometric data- changes increase in amplitude for fainter sets suffer from biases that can be The repeat observations from the SDSS objects. Similar trends are found in revealed, modelled and corrected with allow us to test our photometric model- the other bands and they are strongest in our methodology. Arguably the most pro- ling procedures using a dataset that the z-band. We find that the trends ductive wide-field multi-waveband survey includes many objects with unknown true range from ~ 7–15 millimag in each band is the Sloan Digital Sky Survey (SDSS). magnitudes. So we decided to apply for objects brighter than 16 mag, to

14 The Messenger 149 – September 2012 l Figure 2. Upper: Systematic trends in The full details of our analysis of the

the u-band aperture magnitude SDSS data are presented in Bramich & measurements as a function of PSF FWHM and object brightness for one Freudling (2012) where we also investi-

LL@F of the detectors in the SDSS camera. gate systematic trends as a function of The black, red and green points corre- other parameters such as subpixel coor- spond to aperture magnitude meas- dinates, and we speculate as to the urements brighter than 16 mag, in the range 16–18 mag and fainter than causes of some of the trends that we 6 L@F 18 mag, respectively. Asterisks repre- have found. sent magnitude offsets that fall outside of the plot range. Lower: Same as the T @ODQ upper panel for the u-band PSF mag- Acknowledgements nitude measurements from the same detector in the SDSS camera. In both We thank Wolfgang Hummel for his helpful com- /2%%6',@QBRDB plots the vertical blue line represents ments. the critical sampling for the SDSS camera. –20 References

g) –10 Bertin, E. & Arnouts, S. 1996, A&AS, 117, 393 ma 0 Bramich, D. M. & Freudling, W. 2012, MNRAS, 424, 1584

g. (m Freudling, W. et al. 2007, The Messenger, 128, 13 10 Landolt, A. 1992, AJ, 104, 340 Moehler, S. et al. 2010, PASP, 122, 93 Δ ma 20 Padmanabhan, N. et al. 2008, ApJ, 674, 1217 Stetson, P. B. 2000, PASP, 112, 925 PSF 30 York, D. G. et al. 2000, AJ, 120, 1579 u 40 0.5 1.0 1.5 2.02.5 3.03.5 Links PSF FWHM (arcsec) 1 The IDL photometric modelling program is available from [email protected] on request 2 All improvements to the pipeline recipes are avail ~ 30–60 millimag and ~ 100–170 milli- camera. The systematic trends for the able in version 4.9.11 of the FORS pipeline at: mag, in the ugri- and z-bands, respec- PSF magnitudes as a function of PSF www.eso.org/sci/software/pipelines/fors/fors-pipe- tively, for objects fainter than 18 mag. FWHM are similar in amplitude to those recipes.hmtl 3 New version of the Stetson photometric catalogue: for the aperture magnitudes but they are http://www2.cadc-ccda.hia-iha.nrc-cn In the lower panel of Figure 2, we present also more complicated and seem to “os- 4 Paranal MeteoMonitor: http://archive.eso.org/asm/ a similar plot for the u-band PSF magni- cillate” as the PSF FWHM increases (the ambient-server tudes for the same detector in the SDSS ug-bands show the clearest examples). ESO/Manu Mejias ESO/Manu

Colour image of the young open cluster NGC 371 in the Small Magellanic Cloud obtained with FORS1. Images in three emission lines – two of helium (Hei 5876 Å and He ii 4686 Å) and one of hydrogen (Ha) – were combined and emphasise the extended Ha emission produced by ionising photons from the hot O and B type stars in the cluster. See eso1111 for more details.

The Messenger 149 – September 2012 15 Telescopes and Instrumentation

Provisional Acceptance of KMOS

Suzanne Ramsay1 powers between 3000 and 4000. A lower conformance to scientific performance. on behalf of the KMOS team resolving power mode allows the H- The instrument on a flexure rig is shown and K- windows to be covered simultane- in Figure 1. ously. Spatially resolved information on 1 ESO 24 sources can be obtained with a single With these tests successfully completed, pointing. Cryogenic arms position pick- the instrument has been released for off mirrors over a 7.2 arcminute field at delivery to Paranal. The cable rotator (on The near-infrared, multi-integral-field the focal plane of the UT1 Nasmyth the right of the figure) needed to support unit spectrograph, KMOS, has passed focus, relaying 2.8 × 2.8 arcsecond fields the KMOS electronics is too large for air an important milestone. The provi- to integral field units. The spatial sampling freight, and so was sent by sea in ad- sional acceptance of this instrument by on sky is 0.2 × 0.2 arcecseconds. KMOS vance of the rest of the instrument. Dur- ESO in summer 2012 was the first has been designed for the scientific goals ing the months of September and Octo- step towards the commissioning of this of understanding the evolution and mass ber KMOS will be reintegrated and new Very Large Telescope facility on assembly of galaxies at moderate red- tested in the Paranal Assembly, Integra- the VLT Unit Telescope 1 (UT1) at the shift, galaxies at extremely high redshift, tion and Test facility before being installed end of November 2012. reionisation and galactic stellar popula- on the Nasmyth platform. First light is tions. planned for the end of November, followed by commissioning periods to con- KMOS has been designed, built and Before provisional acceptance was firm the instrument performance on-sky tested by a consortium consisting of awarded, extensive testing was carried and to ensure that the system is fully Durham University, the Max-Planck- out in the integration laboratory at the integrated into the Paranal Observatory. Institut für extraterrestrische Physik UK Astronomy Technology Centre (see Astronomers can look forward to a first (MPE), Universitäts Sternwarte München Sharples et al., 2010). ESO instituted a call for proposals with KMOS in March (USM), Oxford University and the UK rigorous Provisional Acceptance Europe 2013 (Period 92). Astronomy Technology Centre (Sharples (PAE) process for this second generation et al., 2005). This unique spectrometer instrument. Over the first six months of covers the wavelength range from this year, ESO staff from Paranal and References 0.8–2.45 μm with five gratings. TheIZ -, Garching worked with the consortium to Sharples, R. et al. 2005, The Messenger, 122, 5 YJ-, H- and K- bands can each be witness and carry out tests that verified Sharples, R. et al. 2010, The Messenger, 139, 24 observed in one setting at resolving the performance in all areas, from safety

Figure 1. KMOS is shown on the flexure test rig in the integration hall at the UK Astronomy Technology Centre.

16 The Messenger 149 – September 2012 Telescopes and Instrumentation

Gearing up the SPHERE

Markus Kasper 1 Nicolas Schuhler 1 intensity while retaining the light from the Jean-Luc Beuzit2 Arnaud Sevin 8 exoplanet. It is mandatory to obtain Markus Feldt 3 Ralf Siebenmorgen1 spectral or polarimetric data of faint (con- Kjetil Dohlen 4 Christian Soenke1 trast lower than about 10–6) exoplanets. David Mouillet 2 Eric Stadler 2 Direct imaging offers important comple- Pascal Puget2 Marcos Suarez1 mentary information to radial velocity Francois Wildi 5 Massimo Turatto 7 studies of exoplanets, such as resolving Lyu Abe 6 Stéphane Udry 5 the sin i ambiguity intrinsic to the radial Andrea Baruffolo7 Arthur Vigan 4 velocity method, and allows for dynamic Pierre Baudoz 8 Gérard Zins 2 mass measurements of individual exo- Andreas Bazzon 9 planets. It can provide additional diag- Anthony Boccaletti 8 nostic data, e.g., through polarimetry, Roland Brast 1 1 ESO and greatly improves observing efficiency Tristan Buey 8 2 Institut de Planétologie et through the ability to confirm a detec- Olivier Chesneau 6 d’Astrophysique de Grenoble, France tion in a couple of nights rather than fol- Riccardo Claudi 7 3 Max-Planck-Institut für Astronomie, lowing an orbit, which may take years. Anne Costille 2 Heidelberg, Germany Alain Delboulbé 2 4 Laboratoire d’Astrophysique de In August 2007, the contract for the con- Silvano Desidera7 Marseille, France struction of SPHERE was signed with Carsten Dominik12 5 Observatoire de Genève, Switzerland a consortium of 11 institutes from five Reinhold Dorn1 6 Laboratoire Lagrange, Nice, France European countries: IPAG (PI institute, Mark Downing1 7 INAF – Osservatorio Astronomico di Grenoble, France); MPIA (Co-PI institute, Philippe Feautrier 2 Padova, Italy Heidelberg, Germany), LAM (Marseille, Enrico Fedrigo1 8 Laboratoire d’Etudes Spatiales et France), LESIA (Paris, France), Lagrange Thierry Fusco11 d’Instrumentation en Astrophysique, (Nice, France), Osservatorio Astrono- Julien Girard 1 Paris, France mico di Padova (Italy), Observatoire de Enrico Giro7 9 Eidgenössische Technische Genève (Geneva, Switzerland), ETHZ Laurence Gluck 2 Hochschule Zürich, Switzerland (Zurich, Switzerland), University of Frederic Gonte1 10 University of Amsterdam, Amsterdam (the Netherlands), ASTRON Domingo Gojak1 the Netherlands (Dwingeloo, the Netherlands), and Raffaele Gratton 7 11 Office National d’Etudes et de ONERA (Châtillon, France). Signing the Thomas Henning 3 Recherches Aérospatiales, Châtillon, contract was quickly followed by the Norbert Hubin1 France preliminary design review in September Anne-Marie Lagrange 2 12 Stichting ASTRonomisch Onderzoek in 2007 and the final design review in Maud Langlois 4 Nederland, the Netherlands December 2008. The assembly, integra- David Le Mignant 4 tion and testing of subsystems at the Jean-Louis Lizon1 various integration sites took almost three Paul Lilley1 Direct imaging and spectral charac years, ending in autumn 2011,W and was Fabrice Madec 4 terisation of exoplanets is one of the concluded by a series of assembly readi- Yves Magnard 2 most exciting, but also one of the most ness reviews. Since the end of 2011, Patrice Martinez 2 challenging areas, in modern astron- SPHERE has been undergoing integra- Dimitri Mawet 1 omy. The challenge is to overcome the tion and testing at IPAG in Grenoble. Dino Mesa 7 very large contrast between the host The fully assembled instrument is now Ole Möller-Nilsson 3 star and its planet seen at very small entering the final test phase and rapidly Thibaut Moulin 2 angular separations. This article reports approaching Preliminary Acceptance Claire Moutou 4 on the progress made in the construc- Europe (PAE). Jared O’Neal1 tion of the second generation VLT Aleksei Pavlov 3 instrument SPHERE, the Spectro- SPHERE (see Beuzit et al. [2006] for Denis Perret8 Polarimetric High-contrast Exoplanet an overview) will provide high imaging Cyril Petit11 REsearch instrument. SPHERE is contrast by combining extreme adaptive Dan Popovic1 expected to be commissioned on the optics (XAO), coronagraphy, accurate Johan Pragt12 VLT in 2013. calibration of non-common path instru- Patrick Rabou 2 mental aberrations and post-observa- Sylvain Rochat 2 tional data calibration through various dif- Ronald Roelfsema12 Direct imaging is presently the most ferential methods. The instrument is Bernardo Salasnich 7 promising technique to efficiently integrated on a large optical table which Jean-François Sauvage 11 reduce the photon noise generated by will occupy the Nasmyth platform A of the Hans Martin Schmid 9 the host star, by suppressing its light VLT Unit Telescope 3. The optical table

The Messenger 149 – September 2012 17 Telescopes and Instrumentation Kasper M. et al., Gearing up the SPHERE

contains all the common-path optics including the XAO module and infrastruc- (1#(2'A@MC#!( ture such as the calibration source mod- (%28' ule. An enclosure will provide thermal 9(,/.+ inertia and stability and will also reduce l local turbulence. Three scientific instruments are attached to this main bench: a differential near-infrared imaging camera and spectrograph (IRDIS, InfraRed S

Dual Imaging Spectrograph); a near- @R infrared low spectral resolution Integral SQ l NM

Field Spectrograph (IFS); and a visible B imaging differential polarimeter (ZIMPOL, m Zurich Imaging Polarimeter).

Figure 1 illustrates the specified and sim- l ulated contrast performance of SPHERE for the different scientific instruments. The differential imaging methods rely either on spectroscopic features (IRDIS) or a certain degree of polarised flux (ZIMPOL) in order to provide the expected l contrast performance. The simulations were performed for very bright stars, so MFTK@QRDO@Q@SHNMǥ the main limitations are residual differ ential aberrations rather than photon Figure 1. The contrast performance of SPHERE for of 6 × 6 pixels each is a suitable and noise. The IFS data are assumed to be its scientific instruments is shown as obtained from well-established technology to achieve simulations (solid lines) before applying angular dif- calibrated by spectral deconvolution ferential imaging techniques. The specified contrast this goal. Very small low spatial frequency (Mesa et al., 2011). Field rotation and performance of the different instruments is shown by wavefront errors, even in the presence potential further contrast improvements crosses. of vibrations, are achieved by efficient tip- by angular differential imaging techniques tilt correction through linear quadratic were not taken into account. Such tech- enough for diffraction-limited images in Gaussian (LQG) control to a level of about niques are expected to make ZIMPOL the optical part of the spectrum. one milliarcsecond root mean square compliant with its contrast requirements. (RMS). Figure 2 shows IRDIS images The HODM can suppress residual wave- recorded in H-band without a corona- front aberrations up to its correction graph. The optically simulated seeing has

Concept and features radius θAO given by the ratio of the a median value of 0.85 arcseconds, assumed wavelength of the observation and the Strehl ratio derived from the cor- SPHERE is built around the XAO system, divided by twice the inter-actuator spac- rected image was 94%. SAXO (SPHERE Adaptive optics for eXo- ing projected back to the telescope aper- planet Observation), which is designed ture (λ/2D). For a wavelength of 1.6 μm The AO-corrected PSF is dominated by as a standard single conjugate adaptive and an actuator spacing of 0.2 metres, the Airy pattern of the telescope aperture optics (AO) unit with many degrees of θAO ≈ 0.8 arcseconds. The intensity of the and shows a ring structure modulated freedom. SAXO incorporates the high- stellar coronagraphic PSF halo is propor- and sprinkled by quasi-static speckles order deformable mirror (HODM) with tional to the power spectrum of residual from residual instrument aberrations with 1377 actuators on a 41 × 41 grid covering aberrations, and their spatial frequency intensity up to 10–3 of the peak intensity the aperture; a high temporal correction defines the angular separation from the at small angular separations. This Airy bandwidth of about 100 Hz is provided PSF centre at which the light is scattered. pattern is then removed by a corona- by ESO’s deep depletion L3-CCD wave- graph, and SPHERE provides a multitude front sensor camera and extremely low Since exoplanets are to be found at small of state-of-the-art coronagraphs such latency SPARTA real-time computer. As angular separations, typically well below as the apodised Lyot coronagraph or the two of the dominant terms in the error 0.5 arcseconds, a very efficient and pre- four-quadrant phase masks with inner budget (fitting error and temporal band- cise correction of low spatial frequency working angles approaching the theoreti- width error) are strongly reduced this aberrations, i.e., the low-order modes, is cal limit of one (λ/D), e.g., Martinez et way, SAXO provides a high Strehl ratio in required to achieve a high-contrast (dark al. (2010). Since stellar coronagraphy is a the near-infrared (NIR) maximising the hole) close to the PSF centre, and is thus quickly evolving research field, future flux intensity in the point spread function a prime objective of SAXO. Its spatially evolutions can be implemented through (PSF) core and hence the exoplanet filtered Shack–Hartmann wavefront sen- exchangeable masks both in the corona- signal. The correction quality is still good sor (SHWFS) with 40 × 40 subapertures graphic focus and in its entrance and

18 The Messenger 149 – September 2012 lenslet array, and each of the spatial pixels (spaxels) is dispersed by either one of two Amici prisms providing spectral resolutions of about 110 and 70 for the two bandpass modes Y–J and Y–H respectively.

ZIMPOL covers the spectral range 600– 900 nm with an image scale of 7 mas for correct sampling at 600 nm wavelength. The instantaneous field of view of 3.58 by 3.58 arcseconds is increased to almost 8 arcseconds in diameter through dithering by internal field selec- tors. The beam is split into two arms by a polarising beam splitter, each arm with its own detector. Differential polarimetry Figure 2. The SPHERE SAXO H-band point spread IRDIS covers a spectral range from in each of the arms is implemented by function is illustrated with the AO loop open (left, 0.95–2.32 μm with an image scale of a ferro-liquid crystal (FLC) modulator that uncorrected image) and with the AO loop closed (right, corrected image). 12.25 milliarcseconds (mas) for Nyquist is synchronised with a row modulation sampling at 950 nm. The field of view of the CCD (every second row is blind exit pupil planes. Finally, residual instru- is permanently split into two channels of thanks to a lenslet array that is mounted mental aberrations will be measured by 11 by 12.5 arcseconds each, both for directly onto the detector, see Figure 4), an evolved phase diversity technique direct and dual imaging. The differential such that each CCD image contains and suppressed to a level of only a few aberrations between the two channels, interlaced images of perpendicular linear nanometres rms by the deformable introduced by the beam splitter and the polarisation states. Filter sets common mirror (DM). Figure 3 shows an H-band individual mirrors, focusing lenses and and separate to the two arms as well as a PSF which has been corrected for the filters, have been carefully minimised to number of calibration devices complete instrumental aberrations and has a 7–10 nm rms total. Both channels are the list of functions. derived Strehl ratio of 99%, consistent projected onto the same Hawaii 2RG NIR with a residual wavefront error of just a detector. Long-slit spectroscopy at A set of three main observing modes few tens of nanometres RMS. resolving powers of 50 and 500 is pro- defines how the light is split between the vided, as well as a dual polarimetric scientific instruments. IRDIFS is the The three scientific instruments will be imaging mode. survey mode which will be used for a fed by the XAO/coronagraphy system and large fraction of the time. In its main con- implement the means for post-observa- The IFS covers the spectral range 0.96– figuration, it combines IRDIS dual imaging tional data calibration techniques. The 1.66 μm again with an image scale of in the H-band with IFS imaging spectros- main parameters of these instruments are 12.25 mas. The 1.73 by 1.73 arcsecond copy in the Y–J bands with pupil stabi- summarised: field of view is sampled by a two-sided lised coronagraphy. Other configurations

Figure 4. The SPHERE ZIMPOL CCD with the cylindrical lenslet array Figure 3. The SPHERE H-band point spread func- mounted on the detection, corrected from residual aberrations, is shown. tor is shown.

The Messenger 149 – September 2012 19 Telescopes and Instrumentation Kasper M. et al., Gearing up the SPHERE

include K-band IRDIS and Y–H band IFS splitting as well as field stabilisation. IRDIS alone can be used to exploit its various modes for more generic NACO- like (viz. high resolution AO imaging) science, while ZIMPOL alone will provide high precision differential and absolute IRDIS polarimetry as well as classical diffraction-limited imaging at optical wavelengths. No mode supports simultaneous NIR and optical observations. IFS

Current status

ZIMPOL SPHERE with all its subsystems has fully been integrated at IPAG in Grenoble. Figure 5 shows the status in early 2012, when the XAO wavefront sensor arm was still not populated, and the main bench was still exposed to the laboratory environment. In the meantime the main enclosure has been installed, and a thermal tent now surrounds SPHERE. Figure 6 shows a detailed view of the SPHERE optical bench with various subsystems and important components indicated. Figure 5. SPHERE in the assembly laboaratory at A detailed status update of the project IPAG with all instruments integrated into the common path. has recently been presented by Beuzit et al. (2012).

The instrument software as well as data reduction and handling software are complete and are used for test data acquisition through template operation De-rotator Deformable mirror and for data analysis by the pipeline. Functional testing has been successful, Spatial filter IFS and SPHERE is now entering the end- to-end performance evaluation with optically simulated turbulence. Major activi- IR coronagraphs ties that are still to be completed are the WFS camera thermal testing of the complete instru- Tip-tilt mirror ment over its specified temperature range between 0°C and 20°C, and the installation and testing of the vacuum cryogenic system, which has many similarities with the one that has been developed for MUSE.

Active toric mirror There are, however, some pending issues which impact on the instrument performance and which will be resolved only in the longer term. The most prominent one is the HODM, which suffers from two main limitations: i) a strongly temperature- dependent shape-at-rest (about 1 μm Figure 6. Detailed view of the SPHERE optical bench peak-to-valley cylindrical wavefront defor- is shown with the main subsystems indicated. The active toric mirror, used to compensate for the mation per degree Celsius); and ii) an HODM temperature-dependent shape-at-rest, is electrical interface incompliance for clearly visible in the centre foreground.

20 The Messenger 149 – September 2012 a number of actuators (currently four found to be out of specification, with one and to experiment with the data reduc- actuators are dead, and several tens of axis not working properly and not achiev- tion tools available at this time. actuators respond more slowly than ing the required amplitude. The DMS is specified, but still on a timescale of a supposed to move the detector by small A workshop dedicated to SPHERE and millisecond). In order to overcome these amounts to cope with bad pixels and its future use is planned for late summer problems, the production of a replace- improve the flat field accuracy, which are 2013; the date will be confirmed depend- ment, HODM2, was launched in 2010. both important, but, at least for AIT, not ing on a successful start of commission- Several modifications to the design en necessarily vital objectives. A replace- ing, possibly followed by a delta call for sure that all SPHERE specifications ment DMS is currently in production and proposals. This workshop will include a are fulfilled. Unfortunately, a number of should be ready for installation at the VLT. dedicated session on ground-based high manufacturing problems have occurred contrast imaging with SPHERE and cover that have delayed the delivery of HODM2 observing proposal preparation and data until October 2013. Because the cylin Releasing SPHERE reduction. drical shape-at-rest of the HODM can be offloaded to a toric mirror (a mirror with The instrument’s preliminary accept- It is foreseen to release SPHERE to the a spherical surface with added astigma- ance in Europe is planned for early spring community during Period 92, and to tism from Zernike terms of third and fifth 2013, immediately followed by shipment include SPHERE in the Period 93 (April– order) in the common path, and the to the Paranal Observatory and on-site September 2014) regular call for propos- actuator deficiencies mainly introduce integration in late spring 2013. With this als for the first time. Starting early 2014, increased photon noise which can be schedule, first light is expected in sum- European astronomers will be able to mitigated by longer exposure times, mer 2013 during the first commissioning carry out spectacular programmes dedi- SPHERE will use HODM1 for its accept- period. Further commissioning periods cated to the detection and charac ance and integration testing (AIT) and, will be carried out later in 2013 during terisation of exoplanets with an unprece- depending on the achieved performance, which the instrument will be operated, dented accuracy. even for installation and commissioning characterised and validated in all possible at the VLT. observing modes. Further objectives of the commissioning period include instru- References Another concern is the degradation of the ment operation through the standard Beuzit, J.-L. et al. 2006, The Messenger, 125, 29 protected silver coatings of several com- procedures and the implementation of Beuzit, J.-L. et al. 2012, Proc. SPIE, 8446 mon path and infrastructure (CPI) mirrors. the data reduction pipeline as well as the Martinez, P., Aller-Carpentier, E. & Kasper, M. 2010, These are being closely monitored and determination of operational efficiency. The Messenger, 140, 10 may require a re-coating at some stage, After the commissioning period, science Mesa, D. et al. 2011, A&A, 529, 131 probably during the period of shipment to verification will be carried out involving Paranal Observatory. Finally, the detector scientists from the ESO community to motion stage (DMS) of IRDIS has been demonstrate SPHERE’s scientifc potential

Two thermal infrared images of Saturn (centre and right) taken with VISIR, and an amateur visible-light

ESO/University of Oxford/L. N. Fletcher/T. Barry image (left) by Trevor Barry for orientation, are shown. The images were taken on 19 January 2011 and show the mature phase of the northern spring hemisphere storm. The centre image (18.7 μm) reveals the structures in Saturn’s lower atmosphere including the storm clouds and its central cooler vortex; the right image (8.6 μm) is sensitive to much higher altitudes in the stratosphere, where emission flanking the central cool region over the storm is observed. See Release eso1116 for more details.

The Messenger 149 – September 2012 21 Astronomical Science found in Release 1235. Release in found and field. The image was formed by combining combining by formed was image The field. WFI whole the occupy stars cluster and 2.2 kpc) M4 is the closest globular cluster (distance telescope. 2.2-metre MPG/ESO the to attached (WFI) Imager Field Wide the 6121) with (NGC taken M4 cluster globular Galactic the of image Colour I -band exposures and more details can be be can details more and exposures -band B -, -, V -

Acknowledgement: ESO Imaging Survey Astronomical Science

New Surprises in Old Stellar Clusters

Ivo Saviane1 first light on 8 December 1908, and eight A few historical notes Enrico V. Held 2 years later it was used by Harlow Shapley Gary S. Da Costa 3 to publish the first paper of his series The practice of using GCs to test the Veronica Sommariva 4 “Studies Based On The Colors And Mag- resolving and light-collecting power of Marco Gullieuszik 2 nitudes In Stellar Clusters”. In the intro- new telescopes and instrumentation con- Beatriz Barbuy 5 duction, he recalled that, “No serious tinued until well after Shapley, and these Sergio Ortolani 6 attempts have been made to determine beautiful objects are still often featured accurate magnitudes, chiefly because in press releases today when new facili- of the lack of dependable magnitude ties are inaugurated. So it is not surpris- 1 ESO scales for the fainter stars.” Such attempts ing that just a handful of years after its 2 INAF – Osservatorio Astronomico di could finally be made thanks to the avail- first light in 1948, the 200-inch telescope Padova, Italy ability of that superb telescope, which at Palomar was used by Arp, Baum & 3 Australian National University, Mt. could collect photometric data of such Sandage (1953) to resolve the faint stars Stromlo Observatory, Australia distant objects as Galactic globular clus- defining the turnoff feature in the colour– 4 INAF – Osservatorio Astrofisico di ters (GCs). magnitude (CM) diagram of M92. It was Arcetri, Italy a breakthrough that suggested the con- 5 University of Sao Paulo, Brazil Among the motivations to undertake his nection between the main sequence 6 University of Padova, Italy work, Shapley quoted the possibility of in the CM diagram of young clusters, and solving the problem of “the order of stel- the later evolutionary phases seen in lar evolution; that is, the probable charac- globular cluster diagrams. Galactic globular clusters have a long ter of the progression of spectral type and distinguished history as conspicu- (color) with age”. Almost one hundred The theoretical interpretation of such ous providers of simple populations years later, this motivation still underlies a diagrams came almost immediately with where models of low-mass stars can be large fraction of stellar cluster studies. the work of Hoyle and Schwarzschild, tested. However their simplicity has In particular globular clusters have been, who, in 1955, were able to calculate a stel- been challenged several times and a and still are, crucial in testing theories lar age of 6.2 Gyr by comparing the track

few peculiar objects have been identi- of low-mass stellar evolution, because of a 1.1 M⊙ star to the CM diagram of the fied. Only recently has the case for ex their stars were born in a single episode, clusters M92 and M3. To be able to per- tended star formation histories become thus representing the simplest conceiv form the analytic calculations, some sim- really compelling, with the unprece- able population. Or at least this has been plifications had to be introduced, so the dented quantity and quality of data from the common wisdom for many years. Hubble Space Telescope imagers and But as observations and data analysis multiplexing spectrographs on large tel- techniques have improved, this view has Figure 1. The fuzzy object above the ESO 3.6-metre escopes. With ages close to that of started to change. This change has been telescope (and the NTT in the foregound) is Omega Centauri, the most massive globular cluster in the the Universe, globular clusters can also helped in part by our work, as we illus- Milky Way. This object was perhaps the nucleus of a help us uncover the earliest phases trate here, after setting things in context. dwarf galaxy that was disrupted several Gyr ago. in the formation of the Milky Way. In both areas, one of the major challenges is to have an abundance ranking of all clusters based on the same metallicity index, and for as many stars as possible inside each cluster; a homo geneous metallicity compilation is only available for about half of all globular clusters. A few years ago we began a project to help close this gap and we report on a few surprising results that are emerging.

In his book Reflecting Telescope Optics Ray Wilson (Wilson, 2004) writes that the 60-inch telescope on Mt. Wilson was, in its time, “arguably the greatest relative advance in astronomical observing potential ever achieved [together with W. Herschel’s 20-foot focus telescope]”, made possible by the technical genius of George Ritchey. The telescope had its

The Messenger 149 – September 2012 23 Astronomical Science Saviane I. et al., New Surprises in Old Stellar Clusters

track was only in qualitative agreement Table 1. Major metallicity compilations. For each reference, NP and NC are the number of programme clus- with the observations. However com ters, and the number of clusters with [Fe/H] homogenised on the same scale. The fifth column lists whether (r)esolved stars or (i)ntegrated light was studied. puters soon became powerful enough to allow numerical calculations, which Reference Acronym NP NC i/r Method were pioneered by Icko Iben and collabo- Searle, L. & Zinn, R. 1978, ApJ, SZ78 19 – r Mean of reddening-free rators. Iben & Rood (1970) were able 225, 357 magnitudes for seven bands Zinn, R. 1980, ApJS, 42, 19 Z80 79 84 i Reddening-independent colour to follow the evolution of metal-poor stars quotient Q39 for objects of different mass, metallicity, Zinn, R. & West, M. J. 1984, ApJS, ZW84 60 121 i EW of Ca ii K line, G-band, Mg i and helium abundance, thus yielding 55, 45 triplet isochrones that could be compared Armandroff, T. E. & Zinn, R. 1988, AZ88 27 – i EW of Ca ii infrared (IR) lines AJ, 96, 92 quantitatively to observed CM diagrams. Rutledge, G. A. et al. 1997, PASP, RHS97 52 70 r EW of Ca ii IR lines The comparison exercise was immedi- 109, 907 ately performed by Sandage (1970) with Carretta, E. et al. 2009, A&A, C09 19 133 r EW of Fe lines in medium- four globular clusters, and his investiga- 508, 695 resolution spectra Harris, W. E. 2010, arXiv, 1012.3224 H10 157 – – Average of literature tion set the foundations for the classic research lines that extend into our times. controversy arose in considerations of which find that up to 80% of the Milky Based on the colour and luminosity of the whether there was an age spread, or a Way could have been formed in situ (e.g., clusters’ turnoffs, Sandage established majority of coeval clusters plus a few de Rossi et al., 2009). an average age of 11.5 Gyr, and cluster- younger ones with possible extragalactic to-cluster age differences formally not origin. To settle the question, a large, Notwithstanding the success of relative greater than ~ 2% (although photometric homogeneous and high quality photo- age studies, they still suffer from one errors allowed an age spread as large metric database of CM diagrams was major problem: in addition to its age, the as one Gyr). The data were not in conflict needed, a task that was becoming possi- luminosity and colour of a star at the with contemporary estimates of the ble at that time thanks to the introduc- turnoff depend on its metallicity, so a key Hubble time, and they were also consist- tion of charge coupled devices (CCDs) as input to relative age studies is a metallic- ent with the rapid-collapse (~ 108 yr) for- detectors into astronomical instrumen ity compilation that is also homogeneous. mation of the Milky Way halo, as pro- tation. Rosenberg et al. (1999) could take their posed by Eggen, Lynden-Bell & Sandage [Fe/H] values from Rutledge et al. (1997), (1962). Globular clusters had thus ac With these detectors, errors better than which was based on homogeneous quired a prominent role both for cosmol- 0.01 magnitudes could be achieved measurements of the equivalent widths ogy and for theories of galaxy formation. at the cluster turnoff, which opened the (EW) of the Ca ii infrared triplet lines. The new perspective also brought ques- way to comparing the position of that The photometric data were collected in tions about cluster and star formation feature — relative to the red giant branch the V- and I-bands because it had been in the primordial Universe, and about sur- or the horizontal branch — in many shown empirically that the V−I colour vival mechanisms against internal and different clusters, with sufficient accuracy difference is much less sensitive to [Fe/H] external disruption processes. to detect age differences of the order than the B−V one (Saviane et al., 1997). of 0.5 Gyr. Because of the small format of However homogeneous [Fe/H] values are those early CCD chips, the fast, post- available for only a fraction of clusters, a A uniform database of metallicities turnoff phases of stellar evolution (the fact that was one of the main motivations horizontal branch in particular) could not for our project. The determination of absolute ages be well sampled, so the photometric col- requires knowledge of cluster distances, our of the turnoff relative to the giant The current state of [Fe/H] data is sum- which are difficult to obtain because branch became the easiest parameter to marised in Figure 2 and in Table 1. The of the paucity in the solar vicinity of pop- be measured. The combination of all largest homogeneous spectroscopic ulation ii standard candles that can be these ideas was behind the Rosenberg et sample of individual stars is still that of calibrated via parallax. Relative ages are al. (1999) study, which was based on a Rutledge et al. (1997) and if we add the comparatively easier to obtain, and there- homogeneous photometric database for clusters of Saviane et al. (2012) then we fore many studies after Sandage tried to 35 clusters, assembled with the 91-centi- find that ~ 55% of objects have a metal- uncover the age distribution of Galactic metre Dutch telescope at La Silla and licity measurement based on the same globular clusters, with mixed results. The the 1-metre Johannes Kapteyn Telescope index (the “reduced” equivalent width of situation was reviewed by Stetson, van (JKT) at La Palma. The conclusion was the Ca ii infrared triplet). We then have den Bergh & Bolte (1996), who concluded that most globular clusters were formed to move to integrated-light spectroscopy, that “as of the current date the state of in a single epoch, but a few objects were to the samples of ZW84 and AZ88 (see the field is still somewhat muddled”, but clearly formed at later stages. Meanwhile Table 1). They are based on the equiva- also hoped that “data now being col- Ortolani et al. (1995) had also found that lent widths of various metallic lines (Ca ii lected by numerous groups in various the Bulge is coeval with the oldest Halo K line, G-band and Mg i triplet), and of sub-disciplines may resolve the remain- clusters. This is consistent with recent the Ca ii infrared triplet, respectively. After ing controversy within a few years”. The simulations of the formation of the Galaxy excluding objects in common with the

24 The Messenger 149 – September 2012 Figure 2. Sources of metallicity for the bility of FORS2: the maximum slit density 157 globular clusters included in the can be reached with the mask exchange Harris (2010) catalogue. Note that more clusters are being discovered by unit, however the lengthy operations of the SDSS and VISTA/VVV surveys. mask manufacture and insertion meant The acronyms are given in Table 1, and that only a few objects per night could in addition: MR = metallicity indices have been observed. Therefore we opted based on medium resolution spectroscopy; HR = [Fe/H] from high resolution for the configurable slits solution, and studies; CM = broadband imaging (CM left the masks for the most compact diagram). The four colour groups indi- objects. cate homogeneous resolved MR spectroscopy (green shades), homogeneous integrated light MR spectroscopy All data were reduced with the FORS2 (blue shades), individual resolved MR pipeline (Izzo et al., 2010) which delivers or HR studies (yellow shades), and no wavelength-calibrated, sky-subtracted spectroscopy or no data (red shades). spectra in an extremely efficient manner; Five clusters in common between AZ88 and ZW84 have been assigned organising the data took more time than to AZ88. Four of the AZ88 and one of reducing them. On the other hand be- the ZW84 clusters have [Fe/H] values cause of the high crowding typical of measured with high-resolution spectra globular clusters, often more than one as well. star per slit was extracted, so a major RHS S12 AZ88 AZ84 part of the work was to cross-check the MR HR CM No data identification of the ~ 600 spectra. Clus- ter members were identified as objects cited studies, these two datasets com- When the first CM diagrams of main with both radial velocity and reduced prise 8% and 12% of clusters, respec- sequence stars based on CCD imaging equivalent widths not deviating signifi- tively. No other homogeneous datasets appeared, they showed a virtually zero- cantly from the average, taking into exist: 12% of clusters have medium or width locus, confirming the visual impres- account that uncertainties in our mean high-resolution spectroscopic data of sion of a smooth, single-age stellar popu- velocities are of order 5–6 km/s. The resolved stars from a variety of sources, lation. However as more and more data fraction of stars that were eventually con- and for another ~ 8% the metallicity accumulated, things started to look less firmed as members varies significantly estimate comes from their CM diagram. simple. In particular, abundance from cluster to cluster, with a median Finally there are a handful of objects for variations have been found for light ele- value of 53% and being always better which no [Fe/H] data exist. ments in all clusters that have been than 20%. Especially for bulge clusters searched so far (see the very recent where field contamination is high, the Rutledge et al. (1997) obtained their spec- review of Gratton et al. [2012]). In addi- catalogues of member stars for follow-up tra with the modest 2.5-metre Dupont tion, a spread in one or more of iron- high-resolution studies is another useful telescope at Las Campanas, so homoge- peak, n-capture, and α elements has also byproduct of our work. neous [Fe/H] data are missing mostly been found for ω Cen, M54, M22, for outer halo or heavily extincted clus- NGC 1851, NGC 2419, Terzan 5 and The equivalent widths of calcium lines in ters. As relative age studies include more NGC 5824. This is particularly interesting red giant stars depend on the Ca abun- and more outer halo objects, we are because it is direct evidence for ex- dance and also on their luminosity, so forced to take metallicities from a variety tended star formation in these clusters. this dependency was removed by adding of sources. For example Marín-Franch et In three of these seven objects the a linear term in V−VHB and obtaining the al. (2009) based their study on the largest spread was discovered or confirmed from “reduced” equivalent width. A calibration homogeneous photometric sample of our FORS2 project. relation from such reduced equivalent Galactic globular clusters (64 objects), widths to the scale (Carretta et al., 2009) but for as many as 25% of them they had was then obtained, with 14 clusters hav- to estimate [Fe/H] from the Zinn & West Improving the situation ing well-determined [Fe/H] values by (1984) compilation of the reddening-inde- high-resolution studies. It was then pendent Q39 photometric index. To sum- In May 2006 we had two observing applied to convert the reduced equivalent marise, for almost half of GCs, the metal- nights assigned to us at the VLT, to col- widths of programme clusters into metallicity values are based on data that are lect medium-resolution FORS2 spectra licity values. These new [Fe/H] values either not spectroscopic, not homogene- for globular clusters whose distance are significantly different from literature ous or not of individual stars. Further- modulus is too large for high-resolution values for about half of our programme more, even when all these conditions are studies, either because of distance or clusters, as graphically illustrated by satisfied, the number of stars measured high extinction. The weather did not help Figure 3, which shows a type of diagram might be too small to look for metallicity us very much, so of the 49 planned tar- first introduced by Zinn (1993). Our new dispersions, precisely the area where gets we could observe only twenty, plus average abundances are lower than liter- globular clusters started to show the first eight calibrators. To increase observing ature values for six clusters (Pyxis, Terzan surprises. efficiency we used the multi-object capa- 3, HP1, NGC 7006, NGC 6569 and

The Messenger 149 – September 2012 25 Astronomical Science Saviane I. et al., New Surprises in Old Stellar Clusters

Figure 3. The metallicity of our pro- 3DQ -&" gramme clusters on the Carretta et al. -&" (2009) scale is plotted here against -&" horizontal branch (HB) type. Isochro- -&" nes are from Rey et al. (2001), and l are separated by 1.1 Gyr, with age +XMF@ decreasing from top to bottom. The -&" -&" oldest isochrone gives the age of clus- -&" '/ l ters at R < 8 kpc (Rey et al., 2001). 3DQ -&" The arrows connect the position of the /XWHR cluster, if [Fe/H] from Harris (2010) %D' -&" is used, to the position given by our 1TO -&" l , metallicity value. -&"

l -&"

l l l !l1! 5 1

Figure 4. The 216 useful spectra of NGC 5824 and foreground stars taken with FORS2 in the calcium triplet region (840–870 nm). The three most prominent lines belong to the Ca ii ion, with wavelengths of 849.8, 854.2 and 866.2 nm.

26 The Messenger 149 – September 2012 NGC 6715), so to retain their horizontal could only have been achieved with of this process have been erased in the branch (HB) morphology they must be the Hubble Space Telescope (HST). By inner parts of the Galaxy, in its halo younger. The higher abundances of measuring stellar magnitudes on archival where dynamical times are long, several Lynga 7, NGC 6558 and NGC 6380 sug- Wide Field Planetary Camera 2 (WFPC2) stellar streams have been identified in gest instead older ages. Zinn had intro- images with his specialised software, the past. There is however still an order of duced the diagram of Figure 3 to see Anderson (2002) discovered that the magnitude discrepancy between the whether the age distribution of Galactic main sequence of ω Cen is split in two. large number of predicted satellites in the clusters would support the extended Multiple stellar populations were subse- Milky Way and the observed ones. halo formation proposed by Searle & Zinn quently discovered in many other clusters, Any addition of a new remnant is there- (1978). In this scenario, our [Fe/H] revi- including those having metallicity disper- fore important to confirm the paradigm. sion would bring more clusters into the sions. The latter are also among the “young halo” class, however the HB mor- most massive in the Galaxy, and some of Under the working hypothesis that clus- phology depends also on the mass loss them appear to be associated with stellar ters with metallicity spreads signpost along the red giant branch (RGB) and streams: M54 (MV = −10.0) is clearly the halo substructures, we have been the helium abundance, so the conclusion nuclear star cluster of the Sagittarius assigned more than 13 hours of addi- will have to be confirmed with precise dwarf galaxy, which is currently being tid- tional FORS2 time in period 89 to extend turnoff photometry. ally disrupted by the Milky Way, and our sample, and potentially to find still

NGC 1851 (MV = −8.3) is surrounded by more unknown examples of these pecu- The second finding of our project is that, an extensive stellar halo that may have liar stellar systems. for three clusters, the dispersion of resulted from the destruction of the dwarf reduced equivalent widths is larger than galaxy in which the cluster was once the measurement error. We thus con- embedded (Olszewski et al., 2009). Acknowledgements firmed the [Fe/H] dispersion of M54 and The completion of this project was significantly fos- discovered a metallicity dispersion in Theoreticians have been able to simulate tered by visits of two members of the collaboration M22 (in parallel with Marino et al. [2009]) ω Cen as the nuclear remnant of a dis- to Padova and ESO. We warmly thank the ESO and probably in NGC 5824. The metallic- rupted dwarf galaxy (Bekki & Freeman, Director General Discretionary Fund for supporting ity distribution of M22 (NGC 6656) has 2003) and Newberg et al. (2009) have them. been discussed in Da Costa et al. (2009), suggested that NGC 5824 (MV = −8.8) where it was found to range from −2.2 may be associated with the newly dis References to −1.2 dex, and to share many proper- covered Cetus Polar Stream (CPS). The ties with those of Cen, including a fast nuclear cluster scenario is quite appeal- Anderson, J. 2002, ASP Conf. Series, 265, eds. ω F. van Leeuwen, J. D. Hughes, G. Piotto, 87 rise to a peak and a broad tail to higher ing because it would offer an explanation Arp, H. C., Baum, W. A. & Sandage, A. R. 1953, AJ, abundances. M22 could be well charac- for the peculiarities illustrated above. If 58, 4 terised because three FORS2 masks a cluster is located in a deep potential Bekki, K. & Freeman, K. C. 2003, MNRAS, 346, L11 were dedicated to this cluster (41 mem- well inside a dwarf galaxy, it might be able Da Costa, G. S. et al. 2009, ApJ, 705, 1481 de Rossi, M. E. et al. 2009, MNRAS, 395, 210 ber stars), while the small number of to retain or to accrete gas, thus forming Eggen, O. J., Lynden-Bell, D. & Sandage, A. R. 1962, stars did not allow us to perform a similar multiple generations of stars or develop- ApJ, 136, 748 detailed analysis for NGC 5824; we could ing chemical anomalies. It is also interest- Gratton, R. G., Carretta, E. & Bragaglia, A. 2012, only estimate a value ≈ 0.11–0.14 dex for ing to note that both M54 and NGC 5824 A&A Rev., 20, 50 Izzo, C. et al. 2010, Proc. SPIE, 7737, 773729 its dispersion. However with observations lie on the same young isochrone in Fig- Marín-Franch, A. et al. 2009, ApJ, 694, 1498 carried out both at Gemini and at the ure 3, and that stars in the nuclei of early- Marino, A. F. et al. 2009, A&A, 505, 1099 VLT in period 87, we were able to collect type dwarf galaxies tend to be younger Monaco, L. et al. 2009, A&A, 502, L9 spectra for a couple of hundred stars, of than the underlying population (e.g., Newberg, H. J., Yanny, B. & Willett, B. A. 2009, ApJ, 700, L61 which more than a hundred were con- Monaco et al. 2009; Paudel et al., 2011). Olszewski, E. W. et al. 2009, AJ, 138, 1570 firmed as cluster members. The data It should be added that metallicity spreads Ortolani, S. et al. 1995, Nature, 377, 701 analysis is in progress, but the new data might be explained by other mechanisms Paudel, S., Lisker, T. & Kuntschner, H. 2011, MNRAS, seem to confirm the presence of a met (e.g., merging clusters with different 413, 1764 Rey, S.-C. et al. 2001, AJ, 122, 3219 allicity spread. Figure 4 shows a montage [Fe/H]), and for these we refer to Gratton Rosenberg, A. et al. 1999, AJ, 118, 2306 of all useful spectra extracted with the et al. (2012). Sandage, A. 1970, ApJ, 162, 841 FORS2 pipeline. Saviane, I. et al. 2012, A&A, 540, A27 In a bigger picture, finding evidence of Saviane, I., Rosenberg, A. & Piotto, G. 1997, in Stellar Ecology: Advances in Stellar Evolution, disrupting satellites in the Galactic Halo eds. R. T. Rood & A. Renzini, 65 Outlook has great significance for the current Searle, L. & Zinn, R. 1978, ApJ, 225, 357 Lambda Cold Dark Matter galaxy forma- Stetson, P. B., van den Bergh, S. & Bolte, M. 1996, The discovery of metallicity dispersions tion paradigm. In this scheme, the Gal- PASP, 108, 560 Wilson, R. N. 2004, Reflecting Telescope Optics .I was greatly advanced by the advent of axy is built up through the merger and Basic Design Theory and its Historical Develop- multiplexing spectrographs at 8–10-metre accretion of lower mass systems, pre- ment, 2nd edn. (Springer) class telescopes, but the other important dominantly at early epochs. Indeed, while breakthrough in globular cluster research the spatial and kinematic signatures

The Messenger 149 – September 2012 27 Astronomical Science

Stellar Populations of Bulges in Galaxies with Low Surface-brightness Discs

Lorenzo Morelli 1, 2 that they can follow a variety of evolution- this scenario, the bulge is formed by the Enrico Maria Corsini 1, 2 ary paths (Bothun et al., 1997). redistribution of disc stars and the gradi- Alessandro Pizzella1, 2 ents that are eventually produced in the Elena Dalla Bontà 1, 2 The typical gas surface density of LSB progenitor disc could either be amplified, Lodovico Coccato 3 discs is below the critical threshold because the resulting bulge has a smaller Jairo Méndez-Abreu 4, 5 necessary for star formation, despite the scalelength than the disc, or could be Mary Cesetti 1, 2 fact that they have a higher content of erased as a consequence of disc heating neutral hydrogen than their HSB counter- (Moorthy & Holtzman, 2006). parts (Galaz et al., 2006). This inability 1 Dipartimento di Fisica e Astronomia, to condense atomic gas into molecular We present a detailed photometric and Università di Padova, Italy gas results in a very low star formation spectroscopic study of a sample of eight 2 INAF–Osservatorio Astronomico di rate and in a significantly slower evolution bulges in LSB discs recently published Padova, Italy of the galaxy. Although most LSB gal by Morelli et al. (2012). The analysis of the 3 ESO axies are bulgeless, there are also galax- spectral absorption lines has allowed 4 Instituto Astrofísico de Canarias, ies with an LSB disc and a significant us to derive the age and metallicity of the La Laguna, Spain bulge component. It is not known whether stellar populations and to estimate the 5 Departamento de Astrofísica, these bulges are similar to those of efficiency and timescale of the last epi- Universidad de La Laguna, Spain HSB galaxies and whether their proper- sode of star formation in order to distin- ties depend on the LSB nature of their guish between the early rapid assembly host discs. and late slow growth of the bulge. The radial profiles of the age, metallicity and α/Fe enhancement of the stellar Invaluable pieces of information that help populations in the bulge-dominated us to understand the processes of for Sample selection, surface photometry region for a sample of eight spiral gal- mation and evolution of bulges in LSB and long-slit spectroscopy axies with low surface-brightness galaxies are imprinted in their stellar pop- stellar discs and bulges are presented. ulations. The central values and radial All the galaxies in this study were se Almost all the sample bulges are char- profiles of age, metallicity andα /Fe lected to be spiral galaxies with a bulge acterised by young stellar populations, enhancement of the stellar component and an LSB disc. The final sample is solar α/Fe enhancements and metal can be used to test the predictions of comprised of eight LSB spiral galaxies, licities spanning from high to sub-solar theoretical models, as has already been with morphological types ranging from values. No significant gradient in age done for the bulges of HSB galaxies Sa to Sm, including some barred galax- and α/Fe enhancement is measured, (Sánchez-Blázquez et al., 2006; Annibali ies. The LSB nature of their discs has whereas a negative metallicity gradient et al., 2007). been confirmed by a detailed photometric is found in a few cases. The stellar decomposition. With this aim, we de- populations of the bulges hosted by low Gas dissipation toward the galaxy rived the photometric parameters of the surface-brightness discs share many centre, with subsequent star formation bulge and disc by applying a detailed properties with those of high surface- and galactic winds, produces a gradient decomposition of the surface brightness brightness galaxies and are therefore in the radial profile of metallicity. There- of the galaxy. We adopted the galaxy likely to have common formation sce- fore, a metallicity gradient is expected in surface photometric 2D (GASP2D) code narios and evolution histories. bulges formed by monolithic collapse by Méndez-Abreu et al. (2008, see Fig- (Kobayashi, 2004), while the metallicity ure 1). The structural parameters of the gradient is expected to be very shallow galaxies were derived assuming the Galaxies with a central face-on surface (or even absent) in bulges built by merg- galaxy surface-brightness distribution to brightness fainter than 22.6 mag per ing (Bekki & Shioya, 1999). Mergers of be the sum of the contributions of a square arcsecond in the B-band are clas- gas-poor galaxies mix up the galactic bulge, a disc and, if necessary, a bar. We sified as low surface-brightness (LSB) stars, erasing the pre-existing population fitted iteratively the model of the sur- systems. Although LSB galaxies are more gradients, and only rarely is the metal- face brightness to the pixels of the galaxy difficult to identify than high-surface licity gradient enhanced by the second- image using a nonlinear least squares brightness (HSB) galaxies, they are not a ary events of star formation, which minimisation. niche phenomenon in galactic astro eventually occur in mergers of gas-rich physics. They constitute up to 50% of the objects. If this latter occurs, a clear The photometric and spectroscopic ob disc galaxy population and, conse- signature can be observed in the age servations were carried out with the quently, they represent one of the major radial profile for several Gyr (Hopkins et Very Large Telescope (VLT) during sev- baryonic repositories in the Universe. al., 2009). The predictions for bulges eral runs between 2001 and 2008 with LSB galaxies are characterised by differ- assembled through long timescale pro- FORS2. For each galaxy the images ent morphologies (ranging from dwarf cesses, such as the dissipationless were obtained with the R_special+76 filter irregulars to giant spirals) and they cover secular evolution of the disc component, and long-slit spectra on the major and a wide range of colours which suggests are more controversial. According to minor axes were usually taken using the

28 The Messenger 149 – September 2012

/&" .ARDQUDC ,NCDK 1DRHCT@KR

- $ @QBRDB

L@F Q BRDB BRDB BRDB @QBRDB @QBRDB @QBRDB

ƅ @Q @Q @Q 8 8 8 L@F L@F l l L@F l Q Q Q ƅ ƅ ƅ l l l l l l l l l l 7@QBRDB 7@QBRDB 7@QBRDB @@QBRDB

Figure 1. Two-dimensional photometric decomposi- brightness measured from FORS2 (dotted line) and tion of PGC 26148. The FORS2 r-band image, best- model image (green solid line). The dashed blue, fitting image, residual (i.e. observed-model) image dash-dotted purple, and dotted red lines represent and surface-brightness radial profile are shown the intrinsic surface-brightness radial profiles of the (panels from left to right). The righthand panel shows bulge, bar and disc, respectively. the ellipse-averaged radial profile of the surface grism GRIS_1400V+18 in combination measured from the flux-calibrated spec- Properties of the stellar populations in the with a 0.7-arcsecond slit that guarantees tra of the eight sample galaxies following central regions an instrumental velocity resolution of Morelli et al. (2004). We also measured 33 km/s at 5000 Å. the average iron index = (Fe5270 + The models of Thomas et al. (2003) pre- Fe5335)/2 and the combined magne- dict the values of the line strength Lick

The stellar kinematics were measured sium–iron index [MgFe]’ = [Mgb (0.72 × indices for a single stellar population as a from the galaxy absorption features pre- Fe5270 + 0.28 × Fe5335)]1/2 (Thomas et function of the age, metallicity and [α/Fe] sent in the wavelength range centred al., 2003). To account for the contamina- ratio. The central values of the velocity on the Hβ and Mg i lines by applying the tion of the Hβ line-strength index by the dispersion, Mgb, Mg2, Hβ, , and gas and absorption line fitting (GANDALF; Hβ emission line, the Hβ index was [MgFe]’ were obtained by a weighted Sarzi et al., 2006) IDL package, adapted measured from the galaxy spectrum after mean of all the measured data points for dealing with the FORS2 spectra. The subtracting the contribution of the Hβ within an aperture of radius 0.3 re for all Mg, Fe and Hβ line-strength indices were emission line. the available spectra. From the central

Figure 2. Distribution of the central values of the Hβ α/Fe enhancements: [α/Fe] = 0.0 dex (solid lines) and [MgFe]’ indices (left panel) and the and Mgb and [α/Fe] = 0.5 dex (dashed lines). In the right panel, indices (right panel) measured over an aperture of the [α/Fe] ratio–metallicity grids are plotted with two 0.3 re for the sample galaxies. The lines indicate the different ages: 2 Gyr (solid lines) and 6 Gyr (dashed models of Thomas et al. (2003). In the left panel, the lines). The green points are the values obtained for age–metallicity grids are plotted with two different three LSB galaxies by Bergmann et al. (2003).

:_%D<l _%D< _%D< :_%D<

:_%D< :_%D< Ä

&XQ :9'<

Ä D ` ' % :9'< &XQ :9'< &XQ :9'< :9'< &XQ :9'< :9'< &XQ :9'< @FD&XQ @FD&XQ :9'< :9'<

:,F%D<Ä ,FAÄ

The Messenger 149 – September 2012 29 Astronomical Science Morelli L. et al., Stellar Populations of Bulges in Galaxies with LSB Discs

Figure 3. Distribution of the mean age (lefthand panel), total metallicity (central panel), and total α/Fe enhancement (righthand panel) for the stellar populations of the bulges of the sample galaxies. The distributions of the same quantities obtained by Morelli et al. (2008) for the bulges of HSB discs are plotted in grey for comparison. For galaxies with sub-solar values of

- α/Fe enhancement, other mechanisms of bulge formation, such as the redistribution of disc material, because of the presence of a bar, or environmental effects need to be considered. The case of the bulge of ESO-LV 4880490 is particularly intriguing. The bulge of this barred galaxy has an intermediate age (3 Gyr), low metallicity, ([Z/H] = −1.07 dex) and sub- l l l FD&XQ :9'<:_%D< solar α/Fe ratio ([α/Fe] = −0.24 dex). These properties are consistent with a slow build-up within a scenario of sec- values of the Lick indices we derived the of a few LSB galaxies (Bergmann et al., ular evolution driven by the bar. mean age, total metallicity and total 2003). The metallicity of the sample α/Fe enhancement of the stellar popula- bulges spans a large range of values from The correlation between the galaxy mor- tion in the central region of the bulge high values ([Z/H] = 0.30 dex) to sub- phological type and the properties of the of the sample galaxies (see Figure 2). solar metallicity ([Z/H] = −1.0 dex). Most bulge stellar population is indicative of the display solar α/Fe enhancements. These possible interplay between the evolution The bulges are characterised by a very properties closely resemble the proper- of the bulge and disc. Thomas & Davies young stellar population, with a distribu- ties of the bulges hosted in HSB galaxies (2006) did not observe any correlation tion of ages peaking at a value of 1.5 Gyr. (Figure 3) and they suggest a formation between the age and metallicity of the They are characterised by ongoing star mechanism with a dissipative collapse stellar population and galaxy morphology formation, confirming previous studies with a short star formation timescale. of the bulge, whereas Ganda et al. (2007) and Morelli et al. (2008) found a mild correlation, with early-type galaxies (S0– S0a) being older and more metal-rich than spiral galaxies (Sa–Sc). Because the above relationships are mostly driven by early-type galaxies, which are lacking in our sample, we do not observe any &XQ correlation between the galaxy morpho- D

@F logical type (Sab–Sm) and the age, metallicity and α/Fe enhancement of our bulges. Nevertheless, we can exclude a strong interplay between the bulge and Q @ disc components. A

< In early-type galaxies and in the bulges of '

:9 l SGHRVNQJ HSB galaxies the metallicity and α/Fe , enhancement are well correlated with the l central velocity dispersion. We find that l Q @ Figure 4. Mean age (upper panel), total metallicity A (middle panel), and total α/Fe enhancement (lower D< panel) of the stellar populations of the bulges of the %

_ sample galaxies as a function of the central velocity : SGHRVNQJ dispersion. In each panel, the red solid and blue l , dashed lines represent the linear regression through l the data points and the correlation found by Morelli et al. (2008) for the bulges of HSB galaxies, respectively. The Pearson correlation coefficient (r) and the KNFm:JLR< coefficients of the linear fit are given.

30 The Messenger 149 – September 2012 also for LSB galaxies the metallicity and α/Fe enhancement correlate with velocity ,DC ,DC ,DC dispersion (Figure 4) and this correlation m m m is consistent with the results obtained in Morelli et al. (2008).

These relations are explained by chemo- dynamical models and cosmological

hydrodynamic simulations of ellipticals - and bulges as the result of a mass- dependent star formation efficiency. Low- mass galaxies have a lower efficiency in converting gas-phase metals into new stars, and this gives rise to a prolonged period of star formation and to lower α/Fe ratios. Our results suggest that this is also true for the bulges of LSB galaxies. We conclude that the most massive l l l l bulges of our sample galaxies are more 6 FD&XQ 6:9'< 6:_%D< metal-rich, and that they are characterised by shorter star formation timescales. Figure 5. Distribution of the gradients of age line represents a Gaussian centred on the median (lefthand panel), metallicity (central panel), and α/Fe value of the distribution, with s reported. The distri- enhancement (righthand panel) for the sample bution of the same quantities obtained by Morelli et bulges. The dashed line represents the median of al. (2008) for the bulges of HSB discs is shown in Properties of the stellar populations in the the distribution and its value is reported. The solid grey for comparison. bulge region

The contamination of the bulge light by sistent with Δ([Z/H]) = 0 (see Figure 5, centre in the lefthand panel of Figure 6. the contribution coming from the under middle panel). Also, the number distribu- Only the bulges of LSB galaxies with lying disc stellar component is a well- tion of the gradients of α/Fe enhance- higher metallicity (−0.1 < [Z/H] < 0.4) are known problem that deserves particular ments has a median Δ[α/Fe] = 0 (Figure 5, consistent with the correlation found by care. To reduce the impact of this effect righthand panel). In all the observed dis- Morelli et al. (2008) for the bulges in HSB in the derived stellar population proper- tributions, most of the deviations from the galaxies and early-type galaxies, respec- ties as much as possible, we evaluated median values can be explained as tively. This is not the case for the few the gradient inside rbd, the radius where a result only of the errors in the estimates remaining bulges with a very low central the bulge and disc give the same con of the gradients. The absence of signifi- metallicity value (−1.1 < [Z/H] < −0.5). If tribution to the total surface brightness cant age and α/Fe gradients is in agree- confirmed with more firm statistics, such (Morelli et al., 2008). This did not com- ment with the earlier findings for early- a result would favour the importance pletely remove the contaminations, but it type galaxies and bulges of unbarred and of dissipative collapse in the assembly of always ensured a similar degree of con- barred HSB galaxies. However, negative bulges (Arimoto & Yoshii, 1987). tamination when comparing the gradients gradients of metallicity are observed in of different galaxies. For each galaxy, the radial profiles of many early-type gal- No correlation has been found between we have derived the Mg2, Hβ, and axies and in the bulges of HSB galaxies. the central value and gradient of α/Fe line-strength indices at the radius rbd. enhancement (see the righthand panel of In the models, the presence of a negative Figure 6). This is in agreement with earlier The corresponding ages, metallicities metallicity gradient predicts a formation findings for early-type galaxies and spiral and α/Fe enhancements were derived by scenario of the bulges in LSB galaxies via galaxies, and it is expected because using the stellar population models of dissipative collapse, when a strong inter- of the absence of gradients in the α/Fe Thomas et al. (2003), as for the central play between the star formation timescale radial profiles of the sample galaxies. values. The gradients of the properties of and gas flows is taken into account in the bulge stellar population were derived order to explain the absence of any α/Fe from the values of age, metallicity and gradient (Pipino et al., 2008). However, The common nature of bulges in LSB and α/Fe enhancement in the radial range out pure dissipative collapse cannot explain HSB galaxies to rbd. All the sample bulges show no the formation of all the sample bulges; age gradient within the error bars, except other phenomena, such as mergers or We have highlighted the fact that bulges for ESO-LV 2060140 and PGC 26148, acquisition events, need to be invoked to hosted by LSB galaxies share many which are characterised by a shallow gra- account for the formation of those bulges structural and chemical properties with dient. In spite of the peak at Δ([Z/H]) = that do not show any metallicity gradient. the bulges of HSB galaxies. Such a simi- −0.15, the median of the number distribu- The metallicity gradients are plotted as larity suggests that they possibly had tion of the metallicity gradients is con a function of the metallicity in the galaxy common formation scenarios and evolu-

The Messenger 149 – September 2012 31 Astronomical Science Morelli L. et al., Stellar Populations of Bulges in Galaxies with LSB Discs

diction requires a detailed comparison between the properties of the stellar populations of both bulges and discs in LSB galaxies. D< '< %

9 References _ : : 6 6 Annibali, F. et al. 2007, A&A, 463, 455 l Arimoto, N. & Yoshii, Y. 1987, A&A, 173, 23 l Beijersbergen, M., de Blok, W. J. G. & van der Hulst, J. M. 1999, A&A, 351, 903 l Bekki, K. & Shioya, Y. 1999, ApJ, 513, 108 Bergmann, M. P., Jørgensen, I. & Hill, G. J. 2003, AJ, l l l l l 125, 116 :9'< :_%D< Bothun, G., Impey, C. & McGaugh, S. 1997, PASP, 109, 745 Figure 6. Gradient and central value of metallicity Coccato, L. et al. 2008, A&A, 490, 589 (lefthand panel) and α/Fe enhancement (righthand Galaz, G. et al. 2006, AJ, 131, 2035 panel) for the sample bulges. In the lefthand panel, Ganda, K. et al. 2007, MNRAS, 380, 506 the dashed blue line represents the linear regression Hopkins, P. F. et al. 2009, ApJS, 181, 135 obtained for the bulges of HSB galaxies by Morelli et McGaugh, S. S. et al. 1995, AJ, 109, 2019 al. (2008). Méndez-Abreu, J. et al. 2008, A&A, 478, 353 Moorthy, B. K. & Holtzman, J. A. 2006, MNRAS, 371, 583 Morelli, L. et al. 2004, MNRAS, 354, 753 tion histories. Our findings are in agree- ties of the bulge of the LSB galaxy ESO Morelli, L. et al. 2008, MNRAS, 389, 341 ment with, and also extend, the previous 323-G064. The fact that bulges hosted in Morelli, L. et al. 2012, MNRAS, 423, 962 Pipino, A., D’Ercole, A. & Matteucci, F. 2008, A&A, results inferred by McGaugh, Schombert galaxies with very different discs are 484, 679 & Bothun (1995) and Beijersbergen et al. remarkably similar, rules out significant Sánchez-Blázquez, P. et al. 2006, A&A, 457, 809 (1999), who compared the photometric interplay between the bulge and disc Sarzi, M. et al. 2006, MNRAS, 366, 1151 properties of the bulges of LSB and HSB components and provides further sup- Thomas, D., Maraston, C. & Bender, R. 2003, MNRAS, 339, 897 galaxies, and by Coccato et al. (2008), port for earlier findings (Thomas & Davies, Thomas, D. & Davies, R. L. 2006, MNRAS, 366, 510 who performed a detailed analysis of the 2006; Morelli et al., 2008). In order to kinematical and mass distribution proper- provide a definite confirmation, this pre- ESO and Joe DePasquale

MPG/ESO 2.2-metre telescope and Wide Field Imager colour picture of the isolated spiral galaxy NGC 3621. Broadband (B and V ) and narrowband emission line ([O iii] and H-alpha) images were combined and highlight the H ii regions and young stars in the spiral arms. NGC 3621 appears to have no bulge and yet its centre harbours an active nucleus; the distance, determined from photometry of Cepheid variable stars, is about 6.2 Mpc. More information can be found in Release 1104.

32 The Messenger 149 – September 2012 Astronomical Science

On the Inside of Massive Galaxies: The Sloan Lens ACS Survey and Combining Gravitational Lensing with Stellar Dynamics and Stellar Population Analysis

Léon Koopmans1 dynamical analyses. This has led to many density slope at the Einstein radius to Oliver Czoske 2 claims of the presence or absence of be measured with an accuracy of typi- dark matter in early-type galaxies (ETGs), cally better than 5% out to redshifts of although some were based on assump- z ~ 1 (Koopmans & Treu, 2002; Treu & 1 Kapteyn Astronomical Institute, tions that were hard to justify (e.g., orbital Koopmans, 2002). The reason is that the Groningen, the Netherlands (an)isotropy). mass enclosed by the Einstein radius 2 Institut für Astrophysik, Universität is accurately determined from the lensing Wien, Austria In recent years, substantial progress has constraints, significantly reducing its been made to remedy these issues, in degeneracy with the orbital anisotropy. particular using integral field spectros- Our understanding of the structure and copy to map the kinematics of galaxies To further and self-consistently combine formation of early-type galaxies (ETGs) (velocities and velocity dispersions) in two these methodologies beyond the early is rapidly evolving, but our inability to dimensions (e.g., ATLAS3D; COMA). techniques, where the only lensing con- disentangle stellar mass from dark mat- However, studies remain confined to the straint used was the mass of the ETG, ter often prevents direct comparison relatively nearby Universe, where ETGs Barnabè & Koopmans (2007) developed of galaxy formation models with obser- can be studied in greater detail and out fully grid-based lensing and two-integral vations without making strong assump- to larger galactic radii than at larger cos- dynamical models that can describe the tions, such as for the initial mass func- mological distances. Studying the cos- combined two-dimensional datasets tion (IMF) or dark matter mass fraction mological evolution of galaxy structure (i.e. the lensed images along with velocity and density profile. As an example, remains out of reach using kinematic/ and velocity dispersion fields) without the increase in mass-to-light ratio (M/L) dynamic techniques alone, at least until the usual assumption of spherical sym- along the Fundamental Plane could be the recently approved European Ex metry or Jeans modelling. The combined partly due to changes in the structure tremely Large Telescope (E-ELT) and its lensing/dynamics analysis yields the total of the ETGs, but also to a change in the equivalents in the US are completed in mass distribution. The final piece of infor- ratio of dark versus stellar mass and ten years time. mation to disentangle the relative contri- even to a change in the stellar M/L with butions of dark and stellar matter in gal- galaxy velocity dispersion (by a steep- At cosmological distances (say z ~> 0.1), axies is stellar population modelling of the ening of the IMF). We report on ongoing massive galaxies may act as gravita- galaxy spectrum, which yields the mass- efforts to disentangle the structure of tional lenses on background sources at to-light ratio of the stars and information early-type galaxies using gravitational higher redshifts. Modelling the shape of on the initial mass function (IMF), ena- lensing, two-dimensional kinematics strongly gravitationally lensed sources bling the light distribution to be converted and stellar population analysis making has become a powerful new tool to to the stellar mass distribution. use of high-resolution images from HST, investigate the structure of the lens gal- integral field spectroscopy from VIMOS, axies. While the total mass within the Powerful techniques require equally good and UVB/VIS spectra from X-shooter. Einstein radius (typically 5–10 kpc at cos- data and much of the effort going into mological distances) can be measured the development of the methods has extremely accurately (to a few percent), been driven by the powerful instrumenta- Background lensing analysis alone also suffers from tion on 8–10-metre-class telescopes. degeneracies, notably the mass-sheet On the VLT, the VIMOS integral field unit Understanding the internal structure of degeneracy, that prevent unambiguous (IFU) instrument has provided two-dimen- massive galaxies, the present-day end- determination of the mass profile. In order sional kinematic data of a large sample products of galaxy formation, as well to break these degeneracies, additional of strong lens systems. More recently, as their evolution over cosmic time is information or a combination of informa- X-shooter has provided exquisite spectral important for understanding galaxy for- tion from several independent methods is data whose broad wavelength coverage mation and the physical processes that required. is ideal for detailed stellar population shape galaxies. analysis. Over the past decade, new techniques One of the roadblocks in these studies have been developed that systematically In this article we describe some results has been the (often) unknown contribu- combine strong gravitational lensing from the Sloan Lens ACS Survey (SLACS; tion of dark matter to the mass distribu- with galaxy dynamics to break the mass- see Figure 1), in particular focusing on tion of galaxies. Historically, galaxy sheet and mass-anisotropy degeneracies the critical contributions of VIMOS and dynamics has been the main diagnostic (see e.g., Koopmans & Treu, 2002; Treu X-shooter toward breaking degeneracies to determine how matter is distributed & Koopmans, 2004). The constraints from in the mass models of ETGs, disentan- in galaxies, but even in the local Universe the two methods are complementary, gling the stellar and dark matter density it has been difficult to disentangle the making their combination particularly profiles and quantifying these as function contributions and relative distributions of powerful in studying galaxy structure. of galaxy mass and redshift. baryonic matter (stars and gas) and dark The combination of a lensing analysis matter; the reason being the notorious with even a single stellar velocity disper- mass-anisotropy degeneracy inherent in sion measurement allows the total mass-

The Messenger 149 – September 2012 33 Astronomical Science Koopmans L., Czoske O., On the Inside of Massive Galaxies

34 The Messenger 149 – September 2012 Figure 1 (opposite page). A subsample of 60 SLACS velocity dispersion of the ETGs comes for anisotropy and the non-spherical nature lens systems. For each system, the left panel shows free from these spectra. Given the red- of ETGs in greater detail, a single velocity a multi-colour HST image and the right panel shows a reconstruction from the best-fitting lens model. shift and the velocity dispersion of the dispersion measurement is not sufficient. ETG, a simple estimate of the Einstein Integral field spectroscopy of 17 SLACS Finding suitable lenses: the Sloan Lens radius can be made. Nearly 100% of the lenses (of which 16 were ETGs) was ACS Survey candidates with an Einstein radius ex- obtained with the VIMOS IFU on the VLT ceeding that of the fibre turned out to be in 2006–2008, as part of a VLT Large Progress in strong gravitational lensing genuine lenses and the overall success Programme (see Figure 2). Fitting of the has often been driven by new instrumen- rate of the HST follow-up programme spectra with stellar templates yielded tation, allowing detailed study of these exceeded 50%. Extensive follow-up with two-dimensional kinematic maps of sys- typically arcsecond-scale systems. The HST has yielded nearly 100 strong gravi- tematic velocity (e.g., due to bulk rotation advent of space-based observatories, tational lens systems with multicolour of the galaxy) and velocity dispersion, in particular the Hubble Space Telescope V-, I- and H-band observations, complete typically out to 1 Reff. These data were (HST), has allowed optical and infrared redshift information and stellar velocity combined with high-resolution HST imag- images with ~ 0.1 arcsecond resolu- dispersions for all systems. A recently ing of the gravitational-lens configuration tion, revolutionising the field. Recently, completed HST snapshot programme and modelled in a fully self-consistent adaptive optics (AO) observations have has yielded another ~50 lens systems way. Although the results are in remark enabled ground-based telescopes to with somewhat lower stellar velocity dis- able agreement (in general within the compete again or even overtake space- persions. This programme has collected errors) with previous results based on based imaging (see e.g., the SHARP pro- the most complete and uniform galaxy- simpler analyses, a much more detailed jects; Lagattuta et al., 2012; Vegetti et scale lens sample to date (Figure 1) with and three-dimensional census was ob- al., 2012). For spectroscopy, 8–10-metre- most lenses being luminous red galaxies tained from the selected 16 ETGs. The class telescopes are without competition. (LRGs). total mass density profiles (Figure 3) IFU observations with the Very Large could be compared with the stellar mass Telescope (VLT) in particular have made it Initial results from combined gravitational density under the assumption of two dif- possible to obtain detailed maps of the lens (mass inside the Einstein radius) and ferent stellar IMFs (Chabrier and Salpeter). kinematic fields of lens ETGs, as we will kinematic data (velocity dispersion inside show. the SDSS fibre) turned out to be a power- The main results that have come out of ful constraint on the total density profile the VIMOS studies are that ETGs genu- Gravitational lenses are rare — only a few (stars plus dark matter) and showed that inely have total density profiles very close hundred are known across the entire sky. these ETGs have mass slopes very simi- to isothermal, but also that there is intrin- Early lens searches targeted potentially lar to isothermal spheres (i.e. flat circular sic scatter between density profiles of lensed background sources, and conse- velocity curves) and similar to those of order 10%, consistent with studies in the quently the properties of the lenses were spiral galaxies. No evolution with redshift nearby Universe. A small but interesting rather heterogeneous. This changed and no correlation with galaxy mass was correlation is found between the density with the advent of the Sloan Digital Sky found in the density profiles, although slope and the stellar mass density, which Survey (SDSS) which took spectra of recent observations may have shown may be a result of their formation (e.g., many millions of targets, among them some minor evolution (Bolton et al., 2012). adiabatic contraction). Another major re- many ETGs that could act as gravitational In addition, and probably just as interest- sult is that, for a fixed IMF along the mass lenses. Based on an earlier idea of ing, was the related work on the Funda- sequence, the deviation between the Warren et al. (1996), the Sloan Lens ACS mental Plane by Bolton et al. (2007), total mass-density profile and that for the (SLACS) collaboration (Bolton et al., 2006) who showed that if one replaces the sur- stars increases rapidly. Assuming the IMF searched systematically through the face brightness within one effective is not varying (this question will be ad- spectra of ETGs in the SDSS database radius (Reff) by the surface mass density dressed later), this implies that the dark- for signs of emission lines coming from derived from lensing and dynamical mod- matter content of ETGs within 1 Reff is not a higher redshift. In these cases the els, then the tilt of the Fundamental Plane only non-negligible but can even domi- 3-arcsecond SDSS fibres ensure a close changes to that derived from the virial nate for the most massive systems, with alignment between a massive ETG and theorem. This finding demonstrates that velocity dispersion s > 300 km/s. a high-redshift source within 1.5 arcsec- these galaxies are homologous (see e.g., onds from the ETG. Because the Einstein Koopmans et al., 2009) and that the tilt is The inferred increase in dark matter con- radius of these systems is often similar to mostly due to a change in the dark mat- tent in the inner parts of ETGs is con the fibre radius, many of them are excel- ter content of these galaxies. sistent with models where feedback in lent strong gravitational lens candidates. creases for increasingly more massive ETGs, either through supernova or active Two more advantages of such a spectro- Two-dimensional kinematic fields: VLT- galactic nucleus feedback (Hopkins et scopic lens search are that the redshifts VIMOS al., 2006). However, it should be kept in of the lens and source will both be known mind that a similar increase can also be without further follow-up, and, in the case To further push the lensing and kinematic caused by a change in the IMF for low- of SDSS, a measurement of the stellar analysis and to assess the effects of mass stars (< 0.5 M⊙; van Dokkum &

The Messenger 149 – September 2012 35 Astronomical Science Koopmans L., Czoske O., On the Inside of Massive Galaxies - - l l l l l l l l l l U NPV m NPV l 61 U NPV m NPV 61 l l l l l l

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Figure 2. Kinematic maps for 17 SLACS lens sys- Conroy, 2010). This could indeed work for of these galaxies to a level that dark mat- tems as derived from VIMOS/IFU observations. For the lower-mass ETGs as can be seen in ter is no longer needed, but in general each system, the left panel shows the systematic velocity (with respect to the mean redshift of the lens Figure 3, because the shapes of the stel- this requires an IMF that is steeper than galaxy), the middle panel the velocity dispersion lar and total density profiles are relative- the Salpeter IMF. In many cases, how- and the right panel the signal-to-noise (S/N) ratios ly similar up to a constant within 1 Reff. ever, scaling of the stellar mass profile of the spectra in the stacked datacube. Kinematic Steepening the low-mass end of the IMF does not match the total density profile, measurements were obtained for spectra with S/N > 8 (per 0.65 Å pixel). From Czoske et al. (2012). could increase the stellar mass content reflecting the fact that a steepening of

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Figure 3. Left: Spherically averaged mass distribu- bination of lensing and dynamics gives lensing data of the Horseshoe lens sys- tions for the 16 early-type galaxies in the SLACS/ very interesting clues. In Treu et al. (2010) tem (Figure 4) as well as spectral energy VIMOS sample, arranged by increasing galaxy mass. The total mass profiles, as derived from the lensing/ it was found that a full analysis of distribution (SED) fitting to disentangle kinematics analysis, are shown by solid black lines. 53 SLACS ETGs indicates that a Salpeter the stellar and dark matter distributions. Stellar mass profiles have been derived for two dif- IMF fits the data best and that “light” Although lighter IMFs are harder to ex ferent IMFs: Salpeter (red) and Chabrier (blue). The IMFs (e.g., Chabrier, Kroupa) can be ex clude due to degeneracies between the dashed black line rescales the luminous mass profile to its maximum value consistent with the total mass cluded. This agreed well with the later stellar and dark matter halo mass distri- distribution (the maximum-bulge hypothesis). result by, for example, van Dokkum & butions, IMFs as steep as Salpeter (slope Right: Dark matter fractions (fDM) versus total mass Conroy (2010) that the spectra of ETGs 2.35) were allowed. Also mass-function enclosed within the three-dimensional effective seem to show absorption-line equivalent slopes steeper than 3.0 were excluded, radius for the 16 early-type galaxies in the sample, computed for Salpeter (red) and Chabrier (blue) widths typical for low-mass stars and thus based simply on the total enclosed mass IMFs. Lower limits for the dark matter fractions were are only consistent with more bottom- within the Einstein radius of the system obtained from the maximum-bulge hypothesis (open heavy IMFs. A complementary analysis as well as the velocity dispersion profile triangles). From Barnabè et al. (2011). by Auger et al. (2010) based on their full (Spiniello et al., 2011). structure seems to confirm that light IMFs the IMF cannot be the sole cause of the are inconsistent with the kinematics of New X-shooter data on the sample of ten change in M/L in ETGs. In fact, models these ETGs. systems continues to be obtained. First with constant M/L can also be excluded results were presented in Spiniello et al. for many other lens ETGs for which Another tantalising result from SLACS (2012) based on one extremely interest- kinematic data are available, showing the was that the IMF seems to steepen with ing XLENS system (Figure 5) that shows strength of combining these two tech- galaxy mass, although this was only very deep Na i and TiO2 lines, which are niques. However, some degeneracies found at the 2s confidence level (Treu both regarded as potential indicators of a between stellar and dark matter mass et al., 2010). In order to investigate this population of low-mass stars (< 0.3 M⊙). remain. effect in greater detail we started the Naively therefore, this system should XLENS survey, which follows up a sub- have a very steep IMF, which can how- sample of ten lenses with X-shooter ever be excluded with high confidence for Stellar populations and the initial mass covering the full ultraviolet to near-infra- slopes exceeding 3.0. Combined with a function: XLENS with X-shooter red (UV–NIR) wavelength range in order larger sample of spectra from the SDSS to measure the equivalent widths of sev- (Figure 5), it was also shown that these

Our ability to measure the stellar IMF of eral absorption lines (Na i, FeH, TiO2, etc.) lines deepen with increasing stellar veloc- these galaxies is one final piece in the that are especially sensitive to low-mass ity dispersion, suggesting some mild puzzle posed by disentangling the frac- stars. Based on a pilot programme, steepening of the IMF, in agreement with tion of the total mass in ETGs that is Spiniello et al. (2011) combined kinematic the work of Treu et al. (2010). Theoreti- contained in dark matter. Again, the com- constraints from X-shooter data with cal work by, for example, Hopkins (2012)

The Messenger 149 – September 2012 37 Astronomical Science Koopmans L., Czoske O., On the Inside of Massive Galaxies

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38 The Messenger 149 – September 2012 seems to be able to explain this result the local Universe. The next generation range down to ~ 150 km/s systems, well based on arguments of gas density dur- of integral field spectrographs both at the below the knee of the mass function of ing star/galaxy formation, but a detailed VLT and the E-ELT will further push the ETGs — we expect even more discover- comparison between observations and limits of applicability of this technique and ies in the coming years that will allow a theory remains to be done. allow the study of the evolution of the complete census of the internal structure, structure of ETGs over a fair fraction of formation and evolution of ETGs and the age of the Universe. the successful SLACS saga to continue. Future work X-shooter will continue to play a crucial Accurate knowledge of the total mass of role as it allows full ultraviolet to near- References a galaxy is essential for disentangling infrared spectral coverage in one go; Auger, M. et al. 2010, ApJ, 721, L163 the distributions of stellar and dark matter this is critical because the data provide Barnabè, M. & Koopmans, L. V. E. 2007, ApJ, 666, within it, as it breaks many of the degen- not only the kinematics (from lines in 726 eracies in mass models based on stellar the optical) but also equivalent widths of Barnabè, M. et al. 2011, MNRAS, 415, 2215 kinematics. The technique of combining absorption lines in the infrared that are Bolton, A. S. et al. 2006, ApJ, 638, 703 Bolton, A. S. et al. 2007, ApJ, 665, 105 kinematics and gravitational lensing has indicators of low-mass stars and hence Bolton, A. S. et al. 2012, arXiv:1201.2988 been used extensively by the SLACS col- can constrain the slope of the IMF. Much Czoske, O. et al. 2012, MNRAS, 419, 656 laboration to arrive at a number of inter- work is currently being done in these Gonzalez, J. J. 1993, PhD Thesis, Univ. California, esting results on the mass profiles of gal- studies worldwide and we expect to Santa Cruz Hopkins, P. F. et al. 2006, ApJS, 163, 1 axies, limits on their dark matter content, be able to make a much stronger state- Hopkins, P. F. 2012, MNRAS, 423, 2037 as well as on the Fundamental Plane and ment in the near future, based on these Koopmans, L. V. E. & Treu, T. 2002, ApJ, 568, L5 the stellar IMF, as discussed in this arti- X-shooter data on a substantial sample Koopmans, L. V. E. et al. 2006, ApJ, 649, 599 cle. More recently this analysis has been of ETGs from SLACS, concerning the Koopmans, L. V. E. et al. 2009, ApJL, 703, L51 Lagattuta, D. J. et al. 2012, MNRAS, 424, 2800 further extended by including constraints contribution of stars (i.e. their IMF) to the Spiniello, C. et al. 2011, MNRAS, 417, 3000 on the stellar IMF from broadband stellar mass of ETGs. These results should Spiniello, C. et al. 2012, ApJ, 753, 32 SEDs and spectra. also shed more light on the tilt of the FP, Treu, T. & Koopmans, L. V. E. 2002, ApJ, 575, 87 as well as on their formation history Treu, T. et al. 2010, ApJ, 709, 1195 van Dokkum, P. G. & Conroy, C. 2010, Nature, 468, Two-dimensional kinematics obtained (and feedback) within massive dark mat- 940 with VIMOS on the VLT in combination ter haloes. Vegetti, S. et al. 2012, Nature, 481, 341 with gravitational lensing has been shown Warren, S. J. et al. 1996, MNRAS, 278, 139 to be powerful at modelling the mass With the recent discovery of ~ 50 more distributions in elliptical galaxies beyond SLACS lenses — extending the mass ESO/SOAR/NASA

This false colour picture of the galaxy cluster ACT-CL J0102−4915 combines R-, i- and z-band images taken with FORS2 on the VLT, griz-band images from the SOAR Telescope and X-ray observations of the hot gas from NASA’s Chandra X-ray Observatory. The galaxy cluster is probably the most massive, hottest, most X-ray luminous and brightest Sunyaev-Zeldovich effect cluster currently known at a redshift greater than 0.6 and so was named El Gordo. See Release eso1203 for more details.

The Messenger 149 – September 2012 39 Astronomical Science

An ALMA Survey of Submillimetre Galaxies in the Extended Chandra Deep Field South: First Results

Mark Swinbank1 of the Extended Chandra Deep Field stage for the evolution of massive galax- Ian Smail1 South are presented. The combination ies at all epochs, and so determining Alex Karim1 of sensitivity and resolution of ALMA their true redshift distribution and contri- Jackie Hodge 2 allows us to precisely pinpoint the sub- bution to the star formation density are Fabian Walter 2 millimetre emission from these galax- basic parameters that are needed to con- Dave Alexander 1 ies to an accuracy of < 0.3 arcseconds. strain galaxy formation models (Baugh Frank Bertoldi 3 In two ALMA submillimetre galaxies et al., 2005). Indeed, since they lie on the Andy Biggs 4 (SMGs) we serendipitously detect bright rapidly diminishing, exponential tail of Niel Brandt 5 [C ii] 157.4 μm emission, yielding red- the mass function, massive galaxies at all Carlos De Breuck 4 shifts of 4.4. This blind detection rate epochs can provide strong tests of gal- Scott Chapman6 within the 7.5 GHz bandpass of ALMA axy formation models as they are often Kristen Coppin 7 is consistent with the previously derived the most challenging systems for galaxy Pierre Cox 8 photometric redshift distribution of formation models to reproduce. Alice Danielson1 SMGs and suggests a modest, but not Helmut Dannerbauer 9 dominant (< 25%), tail of 870 μm se- However, measuring the redshifts for a Alastair Edge1 lected SMGs at z > 4. complete and unbiased sample of SMGs Rob Ivison10, 11 is not trivial: the poor resolution of single- Thomas Greve12 dish submillimetre telescopes, ~ 18 arc- Kirsten Knudsen13 Background seconds, means that there are many Karl Menten2 possible counterparts responsible for James Simpson1 A significant fraction of the obscured star submillimetre emission. SMGs have Eva Schinnerer 2 formation at redshift z > 1 arises from therefore to be identified through correla- Julie Wardlow 14 the most luminous galaxies: ultralumi- tions between their submillimetre emis- Axel Weiss2 nous infrared galaxies (ULIRGs) with sion and that in other wavebands where 15 12 13 Paul van der Werf bolometric luminosities of > 10 –10 L⊙ higher spatial resolution is available, usu- and implied star formation rates (SFR) ally the radio and/or mid-infrared (e.g.,

of > 100–1000 M⊙/yr. Their very low Ivison et al., 2007). These identifications 1 Institute for Computational Cosmology, space densities means ULIRGs are a are probabilistic as they rely on empiri- University of Durham, United Kingdom negligible element of the star-forming cal correlations that have both significant 2 Max-Planck-Institut für Astronomie, population at z ~ 0, contributing < 1% of scatter and which may evolve with red- Heidelberg, Germany the total SFR density. However, the situa- shift. In submillimetre surveys, typically 3 Argelander-Institut für Astronomie, tion at high redshift is very different: the 30–50 % of SMGs lack robust counter- Bonn, Germany first deep, single-dish bolometer surveys parts in the radio or mid-infrared and 4 ESO in the 870 μm atmospheric window un- these may represent either an unidenti- 5 Pennsylvania State University, covered a significant population of dusty fied tail of high-redshift SMGs, or galax- University Park, USA starbursts (e.g., Smail et al., 1997), with ies whose submillimetre emission is rela- 6 Institute for Astronomy, Cambridge, SFRs > 1000 M⊙/yr. These galaxies are tively bright compared to the radio/ United Kingdom some of the brightest sources in the mid-infrared. The latter includes SMGs 7 Dept. of Physics, McGill University, submillimetre waveband and so are fre- with colder than average dust tempera- Montréal, Canada quently called submillimetre galaxies. tures, which may include the isolated, 8 IRAM, Saint Martin d’Hères, France gas-rich disc galaxies. Thus these biased 9 Institut für Astronomie, Universität This 870 μm high-redshift population may identifications may miss precisely those Wien, Austria host up to half of the star formation SMGs that are critical for testing the 10 UK Astronomy Technology Centre, occurring at z ~ 2 (Chapman et al., 2005; models. Edinburgh, Scotland Wardlow et al., 2011) and may be linked 11 Institute for Astronomy, University of to the formation of massive local elliptical To circumvent this problem requires iden- Edinburgh, Scotland galaxies (Genzel et al., 2003; Swinbank tifying the submillimetre emission directly 12 University College London, United et al., 2006). Moreover, the highest-red- using submillimetre interferometers, but Kingdom shift SMGs (z > 4), have also been linked until recently their sensitivity has been too 13 Onsala Space Observatory, Chalmers to the formation epoch of massive, “red low to locate large numbers of SMGs University, Sweden and dead” galaxies at z ~ 2 which are (Smolčić et al., 2012). However, with the 14 Dept. of Physics and Astronomy, now being found in large numbers (e.g., commissioning of the Atacama Large University of California Irvine, USA Whitaker et al., 2012). The progenitors of Millimeter/submillimeter Array (ALMA), we 15 Leiden Observatory, the Netherlands these z ~ 2 red and dead galaxies must can now construct the large samples of have formed the bulk of their stellar pop- precisely located SMGs needed to unam- ulations at z > 4 and the necessary SFRs biguously study their properties and test

Sensitive ALMA submillimetre maps ~ 100–1000 M⊙/yr correspond to the galaxy formation models. of a sample of 122 870 μm selected bright submillimetre galaxy population. If submillimetre sources from our survey true, then SMGs are a key evolutionary

40 The Messenger 149 – September 2012 The ALMA LESS (aLESS) survey metre emission (to within < 0.3 arcsec- (Karim et al., 2012) However, we find an onds), without recourse to statistical exception: all of the brightest submilli We have recently undertaken an ALMA radio/mid-infrared associations. Whilst a metre sources in the LESS sample (with

Cycle 0 study of the 126 submillimetre large number of the radio and/or mid- S870 μm > 10 mJy) actually consist of sources from the 870 μm LABOCA sur- infrared counterparts from previous sta- emission from multi-ple SMGs, each with vey of the Extended Chandra Deep Field tistical associations are confirmed, in a 870 μm fluxes of 3–4 mJy, significantly South (the LESS survey of Weiss et al., significant number of instances the previ- steepening the 870 μm counts above 2009) conducted with the Large APEX ous counterparts have been shown not ~ 8 mJy (Karim et al., 2012). Bolometer Camera (LABOCA) on the to be SMGs. Our ALMA maps turn up Atacama Pathfinder Experiment Tele- new counterparts to previously unidenti- scope (APEX). Despite the short integra- fied submillimetre sources, as well as The highest redshift SMGs tion time per source (~ 2 min), our ALMA multiple SMG counterparts to LABOCA maps are typically ~3 times deeper sources in a number of cases (Hodge As an initial step in our analysis of the

(s870 ~ 0.4 mJy) than the original LABOCA et al., 2012). For the first time, this ALMA ALMA data of the LESS SMGs, we also survey and critically the angular resolu- study provides us with a unique and exploited the frequency coverage of tion is more than an order of magnitude unbiased sample of SMGs with direct our observations to search for emission higher, with a full width at half maximum identifications from the submillimetre with lines in the datacubes. In two SMGs, (FWHM) of 1.4 arcseconds. which we can study the multi-wavelength aLESS61.1 and aLESS65.1 we identi- properties in an unbiased manner (Simp- fy the redshifted [C ii] 157.4 μm emission This combination of sensitivity and reso- son et al., 2012; Smail et al., 2012). Ani- line, indicating redshifts of 4.419 and lution precisely locates the SMGs directly mations of these ALMA observations of 4.445 respectively (see Figure 2 and (see examples in Figure 1), pinpointing the Extended Chandra Deep Field South Swinbank et al., 2012). Both of these the source(s) responsible for the submilli- can be viewed 1. SMGs are very faint at all other wavelengths: both have radio (1.4 GHz) 3s Figure 1. Examples of 345 GHz (870 μm) ALMA We use the sources detected in these upper limits of < 25 mJy and are blank in maps of eight of the SMGs in our ALMA LESS sam- maps to derive the first reliable counts of the Herschel maps at 250, 350 and ple. In each map we identify all of the SMGs (with faint SMGs free from the effects of confu- 500 μm; i.e. they are so-called 870 μm signal-to-noise > 4s) by large squares. The contours on each map start at 4s and are incremented by 2s sion. These counts agree broadly with peakers. Although based on only two (and the 1s value is given in the bottom left corner of those derived from lower resolution single- sources, the blind detection rate of [C ii] in each panel). We also show the primary beam (circle). dish surveys, demonstrating that the the 7.5 GHz (Δz = 0.12) bandpass of Each map is 40 arcseconds across. The ALMA data bulk of the submillimetre sources are not ALMA is consistent with the previously unambiguously locates the SMG counterpart(s) to a precision of < 0.3 arcseconds and to flux limits of caused by the blending of emission derived photometric redshift distribu- ~1.5 mJy. from several, significantly fainter sources tion of SMGs (Wardlow et al., 2011) and

m L)X m L)X m L)X m L)X

The Messenger 149 – September 2012 41 Astronomical Science Swinbank M. et al., An ALMA Survey of Submillimetre Galaxies

suggests a modest, but not dominant, 6@UDKDMFSG§L Figure 2. ALMA spectra of aLESS65.1 (< 25 %) tail of 870 μm selected SMGs at and aLESS61.1, extracted at the posi- @+$22 tion of the peak submillimetre emis- z > 4. sion from the SMGs. From the spectra, we identify the [C ii] 157.4 μm ii emission lines in the upper sideband Since the [C ] emission line is the dominant cooling line within the interstellar which we attribute to [C ii] emission at z = 4.419 and z = 4.445 for aLESS61.1 medium (the [C ii] emission line can com- L)X W and aLESS65.1, respectively. prise ~1% of the total bolometric lumi- %KT nosity of a galaxy), we can use the data to investigate the properties of the interstellar medium (ISM) in the galaxies. In local luminous-infrared galaxies, the l @+$22 ratio of L[C ii] /LFIR is approximately constant at ~1%, but decreases to < 0.1% in local ULIRGs (Figure 3, left). However, the [C ii] detections in high-redshift ULIRGs and active galactic nuclei (AGNs) L)X have shown that the [C ii] emission can W be as bright as in local, low luminosity %KT galaxies. This has been interpreted as due to the lower ionisation field arising from more widely distributed star forma- l tion activity within these systems, in contrast to the compact nuclear star for- %QDP&'Y mation seen in low-redshift ULIRGs. From our ALMA observations, the ratio of

L[C ii] /LFIR in these SMGs is also much higher than seen for similar far-infrared [C ii] emission over a redshift range of Figure 3. Left: The ratio of the [C ii] to far-infrared luminosity (L /L ) as a function of the far-infrared luminous galaxies in the local Universe Δz = 0.12 at z = 4.4 (a co-moving volume [C ii] FIR 5 3 luminosity for aLESS61.1 and aLESS65.1 compared (Figure 3, left). We attribute this to the of 2.9 × 10 Mpc ). Finding two galaxies to local star-forming galaxies and ULIRGs. This figure ii more extended gas reservoirs in these in this volume with bright [C ] emission shows that the ratio of L[C ii] /LFIR for high-redshift high-redshift ULIRGs. In aLESS65.1 the indicates an increase > 1000 times in the ULIRGs is a factor ~10 times higher given their far- infrared luminosities compared to those at z ~ 0. [C ii] emission shows extended emission number density of luminous [C ii] emitters Right: The [C ii] luminosity function at z = 4.4 from our on > 3 kpc scales. from z ~ 0–4.4 (Figure 3). This is equiva- survey compared to z = 0. For the z = 4.4 luminosity lent to a [C ii] luminosity evolution of a fac- function, we assume that all of the [C ii] emitting gal- We also use the volume probed by our tor ~ 3–4 times between z = 0 and 4.4, axies in the Δz = 0.12 volume covered by our obser- ALMA survey to investigate the bright end consistent with the evolution in the far- vations were detected and so these calculations yield only a lower limit on the volume density of high- ii of the [C ] luminosity function (Figure 3, infrared luminosity function over the same redshift [C ii]. right). Our ALMA observations cover the redshift range.

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42 The Messenger 149 – September 2012 Prospects immense starburst activity, their stellar Ivison, R. et al. 2007, MNRAS, 380, 199 and gas masses and dynamics can be Narayanan, R. et al. 2009, MNRAS, 400, 1919 Simpson, J. et al. 2012, MNRAS, in prep. These early results show that ALMA can addressed, and hence the evolution of a Smail, I. et al. 1997, ApJ, 490, 5 trivially identify large samples of SMGs population which have been proposed Smail, I. et al. 2012, MNRAS, in prep. in short exposure times, measure blind as the formation epoch of today’s mas- Smolčić, V. et al. 2012, ApJS, 200, 10 redshifts through the detection of fine sive galaxies — the luminous ellipticals. Swinbank, M. et al. 2006, MNRAS, 371, 465 Swinbank, M. et al. 2012, MNRAS, submitted structure lines and spatially resolve the Wardlow, J. et al. 2011, MNRAS, 415, 1479 dust and gas within the galaxies on ~ kpc Weiss, A. et al. 2009, ApJ, 707, 1201 scales. Constructing large and unbiased References Whitaker, K. E. et al. 2012, ApJ, 745, 179 samples of SMGs with ALMA in a single Baugh, C. et al. 2005, MNRAS, 356, 1191 well-studied field are crucial to investigate Brauher, J. et al. 2008, ApJS, 178, 280 Links the unbiased redshift distribution and Chapman, S. et al. 2005, ApJ, 622, 772 the nature of these galaxies. Topics such Genzel, R. et al. 2003, ApJ, 584, 633 1 Fly-through animations of the ALMA observations: as the triggering mechanisms for their Hodge, J. et al. 2012, MNRAS, in prep. http://astro.dur.ac.uk/~ams/ALMAmovie/ Karim, A. et al. 2012, MNRAS, submitted ) twanight.org ESO/B. Tafreshi (

A recent image showing some of the growing number of ALMA antennas on Chajnantor pointing towards the Milky Way. See Picture of the Week 28 May 2012.

The Messenger 149 – September 2012 43 Astronomical Science

Chemical Properties of a High-z Dusty Star-forming Galaxy from ALMA Cycle 0 Observations

Tohru Nagao1, 2 and chemical properties of galaxies is Roberto Maiolino 3 difficult (see, e.g., Maiolino et al., 2008). In Carlos De Breuck 4 addition, galaxies in their growth phase DUFVHF aNSF Paola Caselli 5 are often enshrouded by a huge amount Bunyo Hatsukade 2 of dust, which makes the restframe op Kazuya Saigo 6 tical diagnostics unusable for such interesting populations of galaxies.

1 The Hakubi Center for Advanced Therefore we have focused on the milli- Research, Kyoto University, Japan metre wavelength band, where we can 2 Department of Astronomy, Kyoto examine spectra of galaxies without University, Japan suffering from serious dust extinction 3 Cavendish Laboratory, University of effects. More specifically, some far-infra- Cambridge, United Kingdom red emission lines, which can be used 4 ESO for diagnosing the physical and chemical 5 School of Physics and Astronomy, properties of galaxies (e.g., Nagao et al., University of Leeds, United Kingdom 2011), are redshifted into the submillime- 6 East Asian ALMA Regional Center, tre and millimetre bands at high-z. There- Figure 1. The ALMA image of the [N ii] 205 μm emis- National Astronomical Observatory of fore millimetre spectroscopy is, in prin sion from LESS J0332 (from Nagao et al., 2012). The size of the white arrow is equal to one arcsec- Japan, Japan ciple, a promising tool to diagnose rapidly ond, equivalent to approximately 6.6 kpc at the dis- growing high-z dusty galaxies. How- tance of LESS J0322. The white ellipse at the left ever, such observations are very chal- bottom shows the ALMA spatial resolution for the The chemical properties of galaxies lenging because the diagnostic fine- observation. provide strong constraints on galaxy structure emission lines are expected to evolutionary scenarios, but diagnosing be very faint. Recently we observed cance (signal-to-noise of ~ 8) at the the chemical properties of high-z dusty LESS J033229.4-275619 (a submillimetre expected frequency, 253.9 GHz (Fig- galaxies by means of optical and near- galaxy [SMG] at z = 4.76, hereafter ure 1). In Figure 2 the resulting ALMA infrared spectroscopy has been chal- LESS J0332) with APEX and detected its [N ii] 205 μm spectrum is compared with lenging. We have therefore focussed on strong [C ii] 158 μm emission (De Breuck the APEX [C ii] 158 μm spectrum, show- far-infrared fine-structure emission lines et al., 2011). This SMG hosts a heavily ing that the measured [N ii] 205 μm flux in high-z dusty galaxies, whose detec- obscured active galactic nucleus (AGN) is only ~4% of the [C ii] 158 μm flux. It is tion is feasible with ALMA. From ALMA according to Gilli et al. (2011), but its surprising that such a faint [N ii] 205 μm Cycle 0 observations, we have detected effects on the emission line spectrum emission was detected with only [N ii] 205 μm emission in a submillimetre are expected to be small. This object 3.6 hours of integration with ALMA, while galaxy at z = 4.76 whose [C ii] 158 μm is an interesting target because its star the [C ii] 158 μm observation required emission has been already detected in formation rate is very high, reaching 14.5 hours of integration with APEX. This –1 our previous APEX observations. The ~1000 M⊙ yr (Coppin et al., 2009). demonstrates the amazing sensitivity of measured flux ratio of [N ii] 205 μm/ However, until recently it has been impos- ALMA, even in Cycle 0. [C ii] 158 μm implies solar metallicity in sible to detect any other fine-structure this galaxy, suggesting a significant lines in this SMG due to the lack of sensi- In order to assess the chemical proper- chemical evolution even at z = 4.76 tivity of previous facilities, thus preventing ties of LESS J0332, we compared the when the cosmic age was only ~1.3 bil- us from investigating in detail the proper- observed flux ratio of [N ii] 205 μm/ lion years. ties of LESS J0332. [C ii] 158 μm with predictions from photo ionisation models. The comparison shows that the chemical composition of One of the main goals of modern astron- ALMA observations of LESS J0332 the gas clouds in LESS J0332 is close omy is to understand the whole picture of to the Solar value, i.e., log(Zgas /Zsun) = galaxy evolution. However, the early Within this context ALMA allowed us to 0.0 +/– 0.4. This is a surprising result, phases of galaxy evolution in the early make a major step forward. In order given the fact that we are observing a Universe are still poorly understood, to assess the chemical properties of rapidly evolving SMG at z = 4.76, where partly because detailed observations of LESS J0332, we proposed to observe the cosmic age was only ~1.3 billion faint high-z galaxies are very difficult its [N ii] 205 μm emission whose ex- years. Since SMGs are thought to be even with largest aperture telescopes pected flux is only a few percent of the progenitors of local massive galaxies, our available, such as the Very Large Tele- [C ii] 158 μm emission. The observa- observational result suggests that mas- scope (VLT). Particularly at z > 3.5, tions were intermittently carried out from sive galaxies had completed their chemi- the most important restframe optical October 2011 to January 2012 with the cal evolution much earlier than less emission lines are redshifted beyond the band 6 receivers and 18 antennas. The massive galaxies. This is consistent with near-infrared atmospheric windows redshifted [N ii] 205 μm emission was the “downsizing” evolutionary picture and therefore diagnosing the physical successfully detected with a high signifi- recently suggested for galaxies, i.e., mas-

44 The Messenger 149 – September 2012 The internal structure of the chemical +HMDRODBSQTLNE:" ((< properties in this SMG is also an interest- .ARDQUDCVHSG /$7 ing issue, because different evolutionary models of galaxies predict different redshift evolutionary scenarios of the spatial metallicity distribution (see, e.g., Cresci et al., 2010). When com-

L)X pleted, ALMA will achieve a sensitivity and a spatial resolution significantly better than the current (already amazing) MFSG capabilities. Future ALMA observations +HMDRODBSQTLNE:- ((< of high-z SMGs, including LESS J0332, NRSQD .ARDQUDCVHSG +, will shed additional light on the early evo-

1@CH lutionary phase of massive galaxies.

References

l Coppin, K. et al. 2009, MNRAS, 395, 1905 Cresci, G. et al. 2010, Nature, 467, 811 l De Breuck, C. et al. 2011, A&A, 530, L8 l l l l Gilli, R. et al. 2011, ApJ, 730, L28 Maiolino, R. et al. 2008, A&A, 488, 463 5DKNBHSXNEKHMD DLHSSHMFF@RJLR Mannucci, F. et al. 2009, MNRAS, 398, 1915 Matsuoka, K. et al. 2011, A&A, 532, L10 Figure 2. The APEX spectrum of the [C ii] 158 μm The obvious next step is to obtain tighter Nagao, T. et al. 2006, A&A, 447, 157 emission (from De Breuck et al., 2011) is compared constraints on the chemical properties of Nagao, T. et al. 2006, A&A, 447, 863 to the ALMA spectrum of the [N ii] 205 μm emission LESS J0332 to discriminate between dif- Nagao, T. et al. 2011, A&A, 526, A149 (from Nagao et al., 2012) from LESS J0332. Nagao, T. et al. 2012, A&A, 542, L34 ferent galaxy evolutionary scenarios. The current large uncertainty in the inferred sive galaxies underwent more evolution in metallicity is due to the fact that we have earlier epochs than less massive galax- measured only two fine-structure lines, ies. Note that the early metal enrichment [C ii] 158 μm and [N ii] 205 μm. Additional in massive systems has also been observations of other lines such as inferred through observations of high-z [O i] 145 μm would give further con- active galactic nuclei such as quasars straints on the physical properties of the and radio galaxies (e.g., Nagao et al., gas clouds in LESS J0332 and, accord- 2006a, 2006b; Matsuoka et al., 2011). ingly, reduce the metallicity uncertainty. ESO/S. Rossi

One of the ALMA 12-metre-diameter European antennas is shown being moved on the antenna transporter during testing at the ALMA Operations Support Facility. See Picture of the Week 16 July 2012 for more information.

The Messenger 149 – September 2012 45 Astronomical News extension project manager, Christoph Haupt, the the Haupt, Christoph manager, project extension HQ Gabor, Hannelore Ms Garching, of town the of mayor the to right): left (from are hammers their ing 11 on 2012. June Apply aceremony in memorated com was building Headquarters ESO to the sion exten new the of stone foundation the of laying The - - - ment 12044 for more information. 2012 June the of copy a was foundations the in placed documents the Among Zeeuw. de Tim General, Director ESO the and Barcons, Xavier Council, ESO the of President See the meeting summary on p. 54. p. on summary meeting the See on Astronomical Telescopes + Instrumentation. Symposium 2012 the SPIE at participants ESO by session poster informal an in participate to tunity oppor the given were Headquarters ESO at Staff Messenger ; see Announce -

- Astronomical News

Report on the ALMA Community Days: Early Science in Cycle 1 held at ESO Headquarters, Garching, Germany, 25–27 June 2012

Suzanna Randall 1 capabilities offered for Cycle 0 were ingly, more than half the participants de- Leonardo Testi 1 rather limited, and comprised only six- scribed themselves as novices in radio/ Evanthia Hatziminaoglou 1 teen 12-metre antennas, very limited submillimetre interferometry, indicating spectroscopic flexibility, and baselines the broad interest in ALMA science. This shorter than ~400 metres. Nevertheless, fully supports the design goal of ALMA, 1 ESO the data quality is already unmatched which from the outset was conceived as by similar (sub)millimetre facilities at the a general community facility with strong same angular resolution, and the first sci- emphasis placed on easy-to-use tools Early Science operations began in Sep- entific publications clearly reveal ALMA’s and widespread user support. tember 2011 and ALMA is now more potential as construction nears comple- than half way through Cycle 0 and con- tion. tinues to gather data of remarkable Technical information quality. The first scientific results based In Cycle 1, the science capabilities on ALMA data include some very inter- offered to the community will be greatly Intended as an introduction to ALMA, esting findings and the number of enhanced compared to Cycle 0, and will the first morning’s presentations started ALMA publications is rapidly increasing. include 32 antennas in the main 12-metre off with an overview of the ALMA con- From the start of Cycle 1 at the begin- array as well as nine 7-metre antennas struction status and the role of the Euro- ning of 2013, the array will be offered to in the Atacama Compact Array (ACA) pean Science Advisory Committee the astronomical community with en- and two 12-metre antennas for the Total (ESAC). This was followed by a recap of hanced science capabilities. The 2012 Power (TP) array. The frequency bands the first year of ALMA science obser ALMA Community Days, summarised offered will be the same as in Cycle 0 – vations and a breakdown of the science here, were held just a few weeks before Band 3 (84–116 GHz, ~ 3 mm), Band 6 capabilities in Cycle 1. the Cycle 1 proposal submission dead- (211–275 GHz, ~ 1.3 mm), Band 7 (275– line and were designed to optimally 373 GHz, ~ 850 μm) and Band 9 (602– The audience were then walked through prepare the European ALMA Commu- 720 GHz, ~ 450 μm). More flexibility in the tools and processes important for nity for Cycle 1 proposal submission. combining continuum and high spectral observing with ALMA, starting with the resolution observations will be offered, ALMA Science Portal 1. This web interface and antenna baselines will reach up to provides all the relevant information and ALMA, the Atacama Large Millimeter/ ~ 1 kilometre. software tools, and allows registered submillimeter Array, is a global collabora- users access to the Helpdesk facility as tion involving Europe, North America, In order to introduce the community to well as information on their ALMA pro- East Asia and the host country Chile. the Cycle 1 capabilities, a 2–3 day work- jects. The software tools pertinent to The array is located on the Chajnantor shop was organised at ESO Garching proposal preparation, the ALMA Simula- Plateau in northern Chile at an altitude of with the aim of optimally preparing the tor Tools and the ALMA Observing Tool, 5000 metres, and when fully completed European ALMA user community for pro- were introduced in preparation for the will comprise at least 66 high-precision posal preparation in Cycle 1. The format practical hands-on tutorials of the follow- antennas equipped to observe in the was similar to that of the previous ESO ing days. While the simulators are used 30 GHz to 1 THz frequency range. ALMA ALMA Community Days held in April 2011 to get a feel for the image that ALMA will has already started to produce trans in preparation for Cycle 0 (see Randall & obtain of an object, taking into account formational results from Early Science Testi, 2011). The first day of the workshop the array configuration and time spent on Cycle 0 programmes and will continue to featured a variety of technical presenta- source, the ALMA OT is used to prepare be the world’s leading observatory at tions giving an overview of the ALMA pro- and submit the actual proposal. It cap- millimetre and submillimetre wavelengths ject, Cycle 1, and the user support availa- tures all the technical information neces- over the coming decades. ble, as well as scientific presentations sary to execute the observations and showing the first ALMA results. The rest determines the setup of the array and the Until the end of construction (foreseen of the workshop was dedicated to hands- correlator for accepted projects. The pro- for 2013) ALMA is being operated in Early on tutorials for the two main pieces of posal review process was then outlined, Science mode, where part of the time software used for proposal preparation: followed by a description of Phase 2 pro- available is used for approved projects the ALMA Observing Tool (OT) and the cesses for highly ranked projects and from the astronomical community, but ALMA Simulator Tools. the quality assurance and data delivery completion and commissioning of the measures taken for executed observa- telescope take priority. Nearly 1000 ob- The ESO ALMA Community Days were tions in Cycle 1. serving proposals from the ALMA Com- part of a coordinated effort by the Euro- munity were received for Early Science pean ALMA Regional Centre (ARC) net- In the afternoon of that same day, the Cycle 0, with an average oversubscrip- work to organise tutorials and webinars technical talks focused on user sup- tion factor approaching ten. The highest for users across the ESO Member States. port provided by the European ALMA ranked projects were scheduled for exe- We welcomed around 80 registered Regional Centre. The European ARC cution in the period from September 2011 participants mostly from Europe, but also together with its counterparts in North through to the end of 2012. The science from as far afield as Australia. Interest- America and East Asia presents the inter-

The Messenger 149 – September 2012 47 Astronomical News Randall S. et al., Report on the ALMA Community Days: Early Science in Cycle 1

'#".l Figure 1. Map of the sequent expensive optical spectroscopy integrated CO line inten- follow-up) was dramatically demon- sity (white contours) and ǥ the velocity field (back- strated. The quick ALMA spectral scans ground image) of the enabled the detection of at least one debris disc HD 21997 as molecular line in 90 % of the submilli ǥ seen by ALMA. The gray metre selected galaxies and two lines ellipse in the bottom left corner shows the syn- (allowing an unambiguous redshift deter- thesised beam. mination) in 50 % of the sample. The ǥ emerging picture is a redshift distribution @S HNM for submillimetre galaxies extending well

DBKHM ǥ beyond the z ~ 2–3 cutoff imposed by the A. Kospal et al. (ALMA Proposal 2011.0.00780.S) selection effect caused by the centimetre

# radio continuum sensitivity in the past.

) ǥ Agnes Kospal (ESA/ESTEC) was a little closer to home with her analysis of the ǥ molecular gas in the debris disc system HD 21997. ALMA’s sensitivity makes it possible to observe the molecular gas l°oǥ abundance and kinematics in this young debris disc, allowing the study of the GLR R R R R )1HFGS@RBDMRHNM early phases of disc dissipation (see Fig- ure 1). Switching back to extragalactic astrophysics, Cinthya Herrera (Institut face between the Joint ALMA Observa- and Band 2 (~80 GHz) receivers. The d’Astrophysique Spatiale) combined tory in Chile and the astronomical com- possibility of supra-THz interferometry is ALMA Science Verification and VLT-SIN- munity. It consists of a coordinating ARC also being studied, along with possible FONI data to trace the Antennae galaxies hosted at ESO and seven ARC nodes upgrades of the existing ALMA compo- merger. The combination of data from distributed across Europe that between nents. the two major ESO facilities in the infra- them provide a variety of services for red and submillimetre allowed the first European ALMA users, including face-to- detection of a compact and very massive face support, Phase 2 support, software First ALMA science results molecular cloud, most likely a precur- development, data reduction and quality sor for extragalactic Super Star Clusters. assurance, as well as the organisation Some spectacular scientific results based Moving to the Solar System, Thibault of community events 2. The ARC also runs on both Cycle 0 projects and Science Cavalié (Laboratoire d’Astrophysique de the Helpdesk facility, which is the official Verification ALMA data were presented Bordeaux) showed impressive maps of point of contact for questions or com- by invited members of the European Saturn’s 2011 storm as seen by Herschel ments specific to ALMA. Additional ser- ALMA community in the science session. and ALMA (see Figure 2). These data vices offered by the ARC include the Matthias Maercker (ESO/Argelander Insti- probe into the planetary atmosphere and development of advanced data modelling tut für Astronomie) presented an analysis can be used to constrain the physical software such as the ARTIST software, of the shell structure of the asymptotic and chemical models for gaseous giants. which was also presented. giant branch star R Scl (see front cover). The ALMA carbon monoxide (CO) obser- Finally, an overview of the Science Verifi- The day of presentations was concluded vations allowed the mass loss of the star cation data taken to date was presented, by an outlook on the long-term develop- in the quiescent phase between thermal including the stunning Band 3 mosaics ment of ALMA science capabilities. In the pulses to be reliably measured for the of the grand design spiral M100 and of medium term, it is expected that the array first time, leading to a reconstruction of the central regions of Centaurus A. The will be equipped with Band 5 (~187 GHz) the mass loss history in the ~ 2000 years first released Band 9 data on IRAS 16293 receivers, originally developed in Europe since the last thermal pulse event. were also shown. as part of an EC-FP6 funded ALMA En- hancement Project. Another development Moving far beyond the realms of the Gal- within the next four years or so will be the axy, Axel Weiss (Max-Planck-Institut für Hands-on software tutorials capability to phase ALMA for incorpora- Radioastronomie) then described his tion into the mm-VLBI (millimetre-Very redshift study of strongly lensed submilli- For the practical software tutorials the Long Baseline Interferometry) network metre galaxies from a Band 3 spectral participants were split into two groups (see the following report on the mm-VLBI scan. The use of ALMA as a stand-alone according to their experience with radio/ workshop on p. 50 ). On a longer time- redshift pinpointer for submillimetre gal- submillimetre interferometry. While the scale, there are plans to equip the array axies (alleviating the need for radio advanced tutorials were designed to be with the low frequency Band 1 (~40 GHz) continuum cross-identification and sub- more compact and last only one day, the

48 The Messenger 149 – September 2012 ǥ JLR ǥ ǥ

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Figure 2. Left: ALMA continuum image of Saturn. Acknowledgements References The rings can also be seen (east and west of the planetary disc in emission, and in front of the planet We would like to thank Christina Stoffer and the ESO Randall, S. & Testi, L. 2011, The Messenger, 144, 39 absorbing part of its emission). The data were Garching IT Helpdesk for their practical support. obtained in ALMA Band 6. Right: CO emission at the We gratefully acknowledge the help of Luca Cortese velocity of Saturn’s Great Storm 2011 remnant (now and Roberto Galvan-Madrid. The tutorials on the Links a huge stratospheric warm vortex). While CO was second day would not have been possible with- detected in emission along the entire atmospheric out the tutors: Andy Biggs, Alan Bridger, Bartosz 1 ALMA Science Portal: www.almascience.org limb, the vortex can easily be discerned as the Dabrowski, Evanthia Hatziminaoglou, Liz 2 More information on the ARC at: http://www.eso. brightest spot on the map (located at ~ 40 degrees Humphreys, Stefanie Mühle and Suzanna Randall org/sci/facilities/alma/arc.html northern latitude). (OT), as well as Steve Longmore, Anaelle Maury, 3 Community Days 2012 website: http://www.eso. Rosita Paladino, Anita Richards, Eelco van Kampen org/sci/meetings/2012/alma_es_2012/program. and Martin Zwaan (Simulators). Finally, we would html like to thank all the speakers for putting so much novice tutorials continued into the third work into their presentations. The workshop was day of the workshop, allowing more time. sponsored by ESO and Radionet, who provided Each group was tutored in the use of travel support to a number of speakers and tutors. both the Simulator Tools and the ALMA OT and started off with a short presenta- tion/demonstration of the tool followed by periods of individual work assisted by tutors (see Figure 3). The novice tutorials included an extensive introduction to submillimetre concepts, the spectral setup and the basics of interferometry, whereas the advanced sessions focused more on the changes since Cycle 0. In total, around 60 participants chose to attend the tutorials.

The feedback received on the Cycle 1 ALMA Community Days was generally very positive, and several of the participants already expressed interest in a similar Cycle 2 workshop. Tutorial material and presentations are available in electronic form on the conference website3. Figure 3. The workshop participants busy at the practical tutorial sessions.

The Messenger 149 – September 2012 49 Astronomical News

Report on the ESO Workshop mm-wave VLBI with ALMA and Radio Telescopes around the World held at ESO Headquarters, Garching, Germany, 27–28 June 2012

Heino Falcke1 quarters in Garching to attend a one and cient phasing of all antennas [Doeleman, Robert Laing 2 a half day workshop on mm-wave VLBI Baudry]. This would effectively allow Leonardo Testi 2 with ALMA and other telescopes. In the the array to be used as a giant single dish Anton Zensus 3 following report on the workshop, the in parallel to its normal interferometric names of speakers are given in square mode. Recording ALMA data and corre- brackets in the text and all of their talks lating it with those of other (sub)milli- 1 Radboud University Nijmegen and are linked to the conference webpage1. metre telescopes would then provide the ASTRON, Dwingeloo, the Netherlands standard ALMA data products as well 2 ESO The reason why the millimetre-wave as super-high resolution images from the 3 Max-Planck-Institut für Radioastrono- region is so important for ultra-high-reso- VLBI mode. mie, Bonn, Germany lution imaging is that heterodyne receivers can still be used and quantum effects ALMA’s wide frequency range (35– do not yet limit our ability to do interfer- 950 GHz, once all of the planned receiver Very long baseline interferometry at ometry, as they do at shorter wavebands are completed) will enable a broad millimetre/submillimetre wavelengths lengths. The addition of ALMA offers a range of VLBI science to be pursued (mm-VLBI) offers the highest achiev- leap in sensitivity, thus making many by astronomers in Europe and around the able spatial resolution at any wave- more and weaker sources accessible to world. It was therefore timely to bring length in astronomy and the inclusion of ultra-high-resolution studies and greatly together interested European astrono- ALMA into a global network will bring improving image fidelity for the brighter mers to discuss their scientific interests unprecedented sensitivity. The work- objects. Only sources with flux densities and ambitions for this new ALMA observ- shop on mm-VLBI reviewed the broad above several hundred milliJansky (mJy) ing capability. The meeting followed range of science topics, from imag- have been observable so far; this thresh- immediately after the Garching ALMA ing the event horizon of the black hole old could be reduced by more than an Community Days. The first part of the at the centre of the Galaxy, through order of magnitude if ALMA were to be meeting included reviews of current activ- masers in the Milky Way and distant included. ities and achievements in mm-VLBI, galaxies to jets in radio galaxies. Plans including the Event Horizon Telescope were laid to develop a science case The phasing up of ALMA as part of a Collaboration, currently being run by and a European organisation to pro- VLBI array had been envisaged from the Haystack Observatory, and the Global mote mm-VLBI including ALMA. beginning of the project and is incorpo- Millimeter VLBI Array coordinated at rated into the system design, but had the Max-Planck-Institut für Radioastrono- been deferred on cost grounds, and in mie in Bonn. The second part concerned The huge potential of very long base- the interests of completing the instrument the potential science that will be enabled line interferometry (VLBI) at millimetre and for stand-alone operation. The ALMA by a VLBI array including ALMA (Figure 1). submillimetre wavelengths is that it Development Steering Committee is now The final discussion centred on upcom- enables the highest resolution imaging considering a proposal by a team of in- ing developments worldwide. Following currently possible at any wavelength stitutions led by the MIT Haystack Ob- in astronomy. The spatial resolution of an servatory in the USA to upgrade the Figure 1. Scientists from all across Europe discuss- interferometer in radians is given by the ALMA correlator and to create the opera- ing mm-wave VLBI science with ALMA in the ESO ratio of the observing wavelength to tional infrastructure needed for the effi- auditorium. the separation of the telescopes. For a wavelength of 1 mm and a separation of 9000 km, this resolution is about 20 microarcseconds. Using ALMA as a phased array to form part of a global VLBI network will offer unprecedented sensitivity at very high angular resolution. This capability will allow the shadow of a black hole, the relativistic jet flows in active galactic nuclei (AGN) and the dusty winds near stellar surfaces to be imaged; and it may potentially even improve measurements of the Hubble constant.

While ALMA is nearing completion and the first observing cycle is under way, astronomers are already thinking ahead along these lines. To discuss the opportunities from a European perspective, over 65 scientists gathered at ESO Head-

50 The Messenger 149 – September 2012 on from the meeting, a science case will be developed, incorporating the ideas presented and discussed.

Approaching the event horizon

One major science case that has been driving the development of sub-mm VLBI has been the possibility of imaging the innermost parts of accretion discs and jets around supermassive black holes and in particular imaging the shadow of the event horizon in the black hole at the Galactic Centre [Falcke, Doeleman]. The shapes and sizes of the shadow and the photon ring surrounding it (e.g., Figure 2) are precisely predicted by Einstein’s theory of general relativity (GR), so this observation would provide tests Figure 2. Simulated images at 345 GHz of the black Mościbrodzka et al. (2009). Left: Face-on orientation; not only of the black hole paradigm but hole in the Galactic Centre using a VLBI array involv- Right: Edge-on orientation. The black hole shadow ing ALMA and other telescopes. The input model is and photon ring are much more difficult to detect, also of GR in its strong-field limit. based on general relativistic magneto-hydrodynamic but still visible in the edge-on case. Figure updated simulations of plasma around a Kerr black hole from from Falcke et al. (2011). The Galactic Centre, Sgr A*, is the most favourable source for this experiment, Powerful jets mation. VLBI at 230 GHz and above since the angular size of its black hole should ultimately reveal the region where shadow on the sky is the largest known The other source of great interest in the jet is formed, thereby addressing one and has optically thin millimetre- and this respect is the black hole in the cen- of the fundamental problems of astro- submillimetre emission on event horizon tral galaxy of the Virgo cluster, M87. physics: jets and discs are ubiquitous in scales. Most importantly, the mass of This black hole is a thousand times fur- astronomical objects ranging from young this source has been determined accu- ther away, but also a thousand times stars to supermassive black holes. rately by near-infrared imaging of the more massive then Sgr A*, so their event stars in the central region of the Milky horizons are comparable in angular size. Moreover, the study of relativistic jets with Way. Ultimately, the mass constraints will In M87, the radio emission is undoubtedly VLBI has recently received additional improve even further with near-infrared produced by a relativistic plasma jet (Fig- attention in connection with observations interferometry, especially the GRAVITY ure 3). Recent mm-VLBI observations of blazars made by the Fermi satellite. project (Eisenhauer et al., 2011). There will [Krichbaum, Hada] indicate that this jet Multi-wavelength campaigns suggest be extremely interesting synergies forms on the scale of a few Schwarzs- that bright gamma flares are directly con- between ALMA VLBI and VLTI in the area child radii, thus imposing extreme connected to outbursts and component of strong-field GR studies [Eisenhauer]. straints on all possible models for jet for- ejections seen at millimetre wavelengths.

Figure 3. Left: 86 GHz VLBI image of al., 2011). Right: A 43 GHz VLBA 0 *09$*+] the jet in M87 (from Krichbaum et al., image from Walker et al. (2008), clearly 2007). The jet extends down to some revealing the limb-brightened structure tens of Schwarzschild radii (Hada et also seen at 86 GHz.

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The Messenger 149 – September 2012 51 Astronomical News Falcke H. et al., Report on the ESO Workshop “mm-wave VLBI with ALMA”

Surprisingly, these flares seem to come Figure 4. Position– &'Y velocity plot showing from rather large distances from the &'Y the observed 22 GHz

&'Y Richards A. black hole, i.e., regions that can still be water vapour emission imaged by mm-VLBI even in more dis- R from the oxygen-rich tant sources, where the event horizon is AGB star IK Tau (colour- L@ too small to resolve [Giroletti, Orienti]. coded by velocity), together with the predicted locations of water O@MRHNM maser emission at 321 Masers in stars, star-forming regions and and 325 GHz from mod- DNEDW AGN SQ els by Malcolm Gray. DM &'Y

Another fascinating science driver at QN millimetre wavelengths is high-brightness SE ERD

line emission. Many of the lines com- .E &'Y monly detected by ALMA are produced in extended and diffuse regions with low brightness temperatures and are not detectable at high spatial resolution. This changes, however, when one looks at 5+21JLR maser emission or at absorption lines towards compact continuum sources [Impellizzeri]. etry of masers [Brunthaler] is also needed wavelengths has been given by the first in the Galactic Centre, where the accu- ALMA test observations of 321 and Well-known examples of maser sources racy of the basic reference frame for cal- 658 GHz water masers with two-kilometre occur in evolved stars, where H20 and culating stellar orbits is limited by errors baselines (Figure 5). The observations SiO masers provide impressively detailed in cross-referencing the radio and optical are part of the initial tests on the longer tracers of the dynamics of the molecular reference frame using SiO masers. baselines and demonstrate the use of and dusty winds blown away from the old compact spectral line sources for calibra- star into the interstellar medium [Colomer, Masers are also seen in star-forming tion. The targets chosen for these initial Richards]. Quite a number of maser lines regions and young stellar objects, par- tests are well known high-mass star- of water and other molecules have fre- ticularly in regions excited by shocks forming regions, which contain bright quencies above 35 GHz. (A list of maser [Goddi]. They may trace radial infall as maser sources, and analysis of the test transitions relevant to VLBI is given in the well as outflow. Again VLBI allows pre- data is still in progress. These early re- contribution by E. Humphreys linked to cise measurement of the dynamics of sults clearly show the potential of ALMA the conference web page). Some of these these processes. and, in the future mm-VLBI, for high transitions are expected to come from angular resolution imaging of bright the most excited molecules close to the A foretaste of the potential of high-reso maser sources. Additional tests are cur- stellar surface (Figure 4). Precise astrom- lution maser observations at millimetre rently being planned targeting masers

W49 H20 maser 321 GHz !@RDKHMDRTOSNL !@RDKHMDRTOSNJL

ǥ ǥ Goddi C.

ǥ ǥ S@ @S HNM @S HNM @ C DBKHM DBKHM ǥ ǥ RS

# Figure 5. ALMA test # D S observations of water- ) ) maser emission from W49N at 321 GHz. ǥ ǥ , + Left: baselines up to 400 metres, with a beam of 0.55 by 0.44 arcseconds. goǥ %HDP ǥ ´ǥ goǥ %HDP ǥ ´ ǥ Right: baselines up to 2 kilometres with G L R R R R R R G L R R R R R R a beam of 0.26 by )1HFGS@RBDMRHNM )1HFGS@RBDMRHNM 0.16 arcseconds.

52 The Messenger 149 – September 2012 in late-type stars. A full characterisation mally located pulsar could, e.g., measure extra level of complexity, such as a yet- of submillimetre maser sources across the black hole mass to one part in a mil- to-be achieved form of dynamic schedul- the sky may also generate an alternative lion and provide independent tests of GR. ing to take account of changing weather network of (bright) phase calibrators for conditions. high frequency observations. Organisational challenges The community’s enthusiasm about the Extragalactic maser sources are also groundbreaking possibilities offered known [Humphreys]. A famous example VLBI inherently requires many telescopes by mm-VLBI with ALMA was clearly evi- is the nearby active galaxy NGC 4258, to operate together. While the ALMA dent during the workshop: some of the where a warped molecular disc sur- phasing project is under way, other milli- expected science results may indeed rounds the central supermassive black metre telescopes will also be needed become transformational. There was gen- hole. VLBI proper motion observations of to act as part of a global array. Existing eral agreement at the conclusion of the 22 GHz water masers in the disc have activities at 3 mm (the Very Long Base- meeting that, from a European perspec- been used to obtain a precise geometric line Array and the Global Millimeter VLBI tive, the ultimate goal of the planning pro- distance to this galaxy, making it a cru- Array) and at 1 mm (the Event Horizon cess should be a facility accessible to cial component of the extragalactic Telescope project) have laid the ground- the general user, with time made avail distance ladder. Currently the water work for future coordinated observa- able through open competition. maser cosmology project is extending tions. Some of the most outstanding sci- this technique to larger distances, ence goals, like imaging the black hole On the way towards this goal, the scien- thereby providing an independent meas- shadow, are unlikely to be achieved with tific needs of the user community for urement of the Hubble constant and a just a few baselines. As ALMA reaches mm-VLBI with ALMA need to be com- direct determination of black hole masses full operation, there will be financial pres- piled as a necessary input to the approval (important for the black hole mass– sures to close down existing facilities, process for the ALMA phasing project. velocity dispersion relation). Observations but on the positive side, new facilities are Some of the technical challenges of this of higher frequency water maser transi- emerging such as the Large Millimeter project are being addressed by the inter- tions (e.g., 183 or 321 GHz) have the Telescope (LMT) in Mexico [Hughes] and national multi-partner phasing-project potential to improve our understanding the Long Latin American Millimeter Array led by the Haystack Observatory: the of the accretion disc physics and geom (LLAMA) in Argentina [Cseh]. In Europe, task for the nascent European ALMA etry. Particularly intriguing is the specula- the Northern Extended Millimeter Array VLBI user community is to organise itself tion that super-masers might exist. In (NOEMA) project, an upgrade of the Insti- to prepare for the successful use of this those systems the millimetre-wave emis- tut de Radioastronomie Millimétrique exciting new capability. sion could be more intense than the well (IRAM) Plateau de Bure Interferometer known 22 GHz line and perhaps detecta- is going ahead [Bremer] and large single The meeting was co-sponsored by ESO ble to greater distances. dishes (IRAM 30-metre, Effelsberg, and Radionet3, an EU Integrated Infra- Sardinia Radio Telescope, Yebes, Onsala structure Initiative to coordinate access, and Metsähovi) will play an important role development and training for radio as- Pulsars, microquasars and gamma-ray at 3 and 7 mm wavelengths. In the USA, tronomy facilities in Europe 2. bursts the Very Long Baseline Array (VLBA) is crucial, as well as the Combined Array Finally, there are many other compact for Research in Millimeter-wave Astron- References sources that are potential targets for omy (CARMA) [Brinkerink], the Submilli Eisenhauer, F. et al. 2011, The Messenger, 143, 16 mm-wave VLBI. In particular, transient meter Telescope (SMT) and Submillimeter Falcke, H. et al. 2011, IAU Symp., 275, 68 sources such as supernovae, gamma-ray Array (SMA) at higher frequencies. Hada, K. et al. 2011, Nature, 477, 185 bursts and microquasars should be very Maitra, D. 2011, IAU Symp., 275, 82 interesting, since the highest frequencies Overall the meeting demonstrated that Krichbaum, T. et al. 2007, Exploring the Cosmic Frontier: Astrophysical Instruments for the 21st probe the earliest phases of any eruption. European astronomers have a broad Century, 189 range of science interests beyond the ini- Mościbrodzka, M. et al. 2009, ApJ, 706, 497 At first sight, pulsar science is an unex- tial key projects that will be addressed Walker, R. C. et al. 2008, Extragalactic Jets: Theory pected field for ALMA, since the radio by a phased ALMA facility alone and in and Observation from Radio to Gamma Ray, ASP Conference Series, 386, 87 spectra of pulsars are usually very steep. coordinated mm-VLBI observations. This Nevertheless, there is some indication might, for example, be organised follow- of spectral flattening at millimetre wave- ing the established examples of the Euro- Links lengths and a phased ALMA should be pean VLBI Network (EVN) supported 1 Workshop webpage: http://www.astro.ru.nl/mmV- able to observe pulsed emission [Kramer]. by the Joint Institute for VLBI in Europe LBI2012 Of particular interest would be searches (JIVE) [van Langevelde], as well as the 2 Radionet3: http://www.radionet-eu.org for pulsars in the Galactic Centre, where Global Millimeter VLBI Array. The inclu- low-frequency pulses suffer from huge sion of ALMA and the extension to higher dispersion and scattering, to the extent frequencies will bring a very substantial that they become undetectable. An opti- improvement in data quality, but also an

The Messenger 149 – September 2012 53 Astronomical News

Some Reflections on the SPIE 2012 Symposium on Astronomical Telescopes + Instrumentation

Jeremy Walsh1 amounts of data on a nightly basis, and other ground-based interferometry facili- Compiled from contributions* mainly geared towards the identification ties and their critical subsystems. There of various types of transients. In the were also presentations of the VLTI visitor current context of global financial difficul- instrument Pionier and the two second 1 ESO ties, maintaining the excellence of oper generation VLTI instruments GRAVITY ations and of support to the community and MATISSE. While space interferometry in an environment of increasingly tight featured less strongly than in previous A very brief summary of the 2012 SPIE resources was a common underlying years, sparse aperture masking showed Symposium on Astronomical Tele- theme. The measurement of scientific an impressive boost in capabilities and scopes + Instrumentation, held in July effectiveness of facilities through biblio- science results. Future prospects for in Amsterdam, is presented from metrics and their importance as a part of interferometric facilities and data reduc- the viewpoint of ESO contributions. the observatory operations chain is tion software were intensively discussed viewed as increasingly important at (during almost a full day) and the, now observatories, including La Silla Paranal. regular, award of the prize in the Inter The 2012 SPIE meeting on Astronomical ferometric Imaging Beauty Contest was Telescopes + Instrumentation (1–6 July The Ground-based and Airbourne Instru- presented. 2012)1 was even larger than the last mentation for Astronomy conference meeting in 2010 in San Diego (see Casali, featured VLT instruments heavily, includ- Given the important role of the SPIE 2010) with around 2300 attendees. It is ing overviews of the ESO instrumentation Astronomical Telescopes + Instrumenta- thus almost impossible to present a com- programme. Separate presentations tion meetings in presenting so many prehensive overview of such a huge of instruments under construction such aspects of ESO’s core activities and to meeting consisting of 12 separate confer- as KMOS, MUSE and SPHERE, those in give those who could not attend a flavour ences, as well as courses and exhibi- plan, such as ERIS, ESPRESSO, MOONS of some of the ESO presentations, an tions. Instead a few reflections collected and 4MOS, and current instruments informal poster session was organised at from some of the ESO participants are undergoing upgrade, such as VISIR and ESO Headquarters on 17 July (see Figure presented. CRIRES, were given. There were exten- on p. 46). Twenty-four posters were sive poster sessions on multi-object in- shown and the presenters were available Not surprisingly ESO staff played a strong struments and planet finders. The instru- for discussion. The topics covered all role in the meeting with more than 100 ment programmes for the three Extra ESO activities from detectors, laser sys- attending, many involved in the pro- Large Telescopes (European Extremely tems, adaptive optics, fibres, instrument gramme committees and a number chair- Large Telescope [E-ELT], Giant Magellan and E-ELT component designs, instru- ing. Mark Casali was Symposium co- Telescope [GMT] and Thirty Meter Tele- ment software control, to operating per- chair and four of the conferences had scope [TMT]) were presented as well as formance monitoring and bibliometrics. ESO chairs — Françoise Delplanke for several of the individual instrument con- The poster session was well attended the Optical and Infrared Interferometry III cepts for the E-ELT. and appreciated by those who did not conference, Suzanne Ramsay for Ground- attend the meeting, and by a few who based and Airbourne Instrumentation for The Adaptive Optics Systems confer- were at the SPIE meeting, but might Astronomy IV, Enrico Marchetti for Adap- ence, not surprisingly, was very heavily understandably have missed something. tive Optics Systems III and Fernando attended with more than 260 contribu- Comeron for Observatory Operations: tions. The most exciting results are com- The next SPIE meeting will be held in Strategies, Processes and Systems IV. In ing from the multi-conjugate adaptive Montreal, Canada in 2014. addition, the speaker at the conference optics (MCAO) systems demonstrating dinner was Jason Spyromillio, who talked exceptional image sharpness over fields on how big telescopes can also make up to 80 arcseconds. The VLT Adaptive References big trouble (for engineers at least). One of Optics Facility (AOF) is currently the Casali, M. 2010, The Messenger, 141, 40 the plenary speakers was also Thijs de most complex system under develop- Graauw from the Joint ALMA Observatory. ment and was well represented. The realms of astronomical science where AO Links The conference on Observatory Opera- makes the greatest mark from Solar Sys- 1 SPIE 2012Astronomical Telescopes + Instrumenta- tions is closest to ESO’s core task of tem science to extragalactic were pre- tion: http://www.spie.org/x13662.xml running a ground-based observatory. sented, not forgetting the Galactic Cen- This year time domain astronomy had an tre. The plans for AO for the three ELTs increased emphasis, motivated by the were featured and a new development of growing numbers of robotic telescopes MCAO for ELTs using natural guide stars and networks producing enormous was outlined.

The conference on Optical and Infrared * Contributions from Fernando Comeron, Françoise Delplancke, Enrico Marchetti and Interferometry strongly featured the exist- Suzanne Ramsay. ing VLTI instruments among those of the

54 The Messenger 149 – September 2012 Astronomical News

Report on the Symposium 30 Years of Italian Participation to ESO held at the Pontificia Università Lateranense, Rome, Italy, 2–3 July 2012 as part of the European Week of Astronomy and Space Science (EWASS 2012) meeting

Vincenzo Mainieri1 been highly beneficial for the scientific community in Italy and has resulted in a large number of outstanding scientific 1 ESO results and publications: 24 out of the 100 most-cited papers from the Paranal Observatory, and 23 out of the 100 most- On 24 May 1982 Italy joined ESO, cited papers from the La Silla Observa- becoming the eighth Member State. In tory have an Italian astronomer as first the past 30 years the participation of author. The first day included also a one- Italy in all of ESO’s endeavours has hour discussion forum where represen been substantial in all respects: people; tatives of different ESO directorates fundamental industrial contributions (Martino Romaniello, Sandro D’Odorico in the construction of telescopes and and Bruno Leibundgut) answered ques- infrastructures; collaboration of insti- tions related to operations, instrumenta- tutes in the development of instrument tion and ESO policies. components; and science programmes. The aim of the symposium was to re- The second day was opened by a review view critically these past achievements talk by Sandro D’Odorico on the Italian and discuss Italian participation in contribution to ESO instrumentation. The future ESO projects. review showed how there has been an increasing involvement of Italian institutes anteed Observing Time (GTO) presented in the past 30 years: from the first con in two contributed talks (Nicola Rosario After a welcome address by the ESO tributions to La Silla instrumentation (e.g., Napolitano and Enrichetta Iodice). Paolo Director General, Tim de Zeeuw, the pro- SUSI2 and WFI), to the involvement in Vettolani, INAF Scientific Director, illus- gramme started with a historical review several first generation (UVES, VIMOS, trated also the plan for the involvement by Giancarlo Setti, which illustrated the FLAMES, FINITO and AMBER) and sec- of INAF in future ESO projects. Finally, reasons why Italy did not join at the time ond generation (X-shooter, SPHERE, the last session of the meeting started of ESO’s foundation in 1962, and de- ESPRESSO) VLT instruments. This posi- with a review talk by Leonardo Testi on scribed the key players, scientists as well tive trend continued in recent years with a ALMA science, followed by several con- as politicians, and the favourable circum- strong participation from Italian institutes tributed talks highlighting important sci- stances that contributed to Italy becom- in E-ELT instrument studies. An important entific results obtained with ESO facilities ing a Member State 20 years later. The Italian contribution was also in the field in the field of metal-poor stars (Elisabetta importance of access to ESO facilities of instrument control software, mostly led Caffau), globular clusters (Raffaele Grat- for the Italian astronomical community by the Astronomical Observatory of ton) and star formation (Matteo Correnti, was stressed by Monica Tosi, as well as Trieste, and Paolo Santin gave a review Fabrizio Massi, Carlo Felice Manara). the significant success rate of Large Pro- talk on this longstanding and fruitful col- gramme proposals with Italian principal laboration with ESO. The proceedings of the meeting will be investigators (PIs). The rest of the first published in the online version1 of Sup- morning was dedicated to the contribu- One of the aims of the meeting was to plements of the Memorie della Società tion of Italian industry to ESO projects. discuss the involvement of the Italian Astronomica Italiana and the presenta- Massimo Tarenghi described the con astronomical community in future ESO tions are available on the symposium tributions connected with the New Tech projects. In the framework of the E-ELT webpage 2. nology Telescope (NTT) and the Very there were four talks on instrument Large Telescope (VLT), while Stefano studies with significant contributions from Stanghellini covered the involvement in Italian institutes: CODEX (Stefano Acknowledgements the European Atacama Large Millimeter/ Cristiani), SIMPLE (Roberto Maiolino), I wish to personally thank the members of the SOC submillimeter Array (ALMA) antenna MAORY (Paolo Ciliegi) and QuantEYE (Magda Arnaboldi, Claudio Cumani, Sandro design and construction. (Roberto Mignani). The afternoon session D’Odorico, Bruno Leibundgut, Alessandro Marconi, of the second day started with a review Gianni Marconi, Nando Patat, Francesca Primas and In the afternoon session there were talk by Giuseppe Bono quantifying the Martino Romaniello) and the EWASS2012 LOC (Giuliana Giobbi and Livia Giacomini) for their help in invited talks on some highlights of extra- impact of ESO facilities on Italian astro- organising this symposium. galactic scientific results obtained by nomical research. With a particular focus Italian astronomers using ESO facilities on the field of stellar astrophysics, it was (presented by Elena Pian, Adriano recognised that access to VLT instru- Links Fontana, Laura Pentericci and Giovanni ments has had a tremendous impact on 1 Online proceedings to be published: http://sait. Cresci), proceeded by a review talk from the scientific output of the Italian astro- oats.inaf.it/Supplementi.htm Alvio Renzini on high impact scientific nomical community. An overview of the 2 Symposium webpage: http://www.eso.org/sci/ papers led by Italian astronomers. The VST project was given by Paolo Vettolani meetings/2012/ewass2012.html access to ESO observing facilities has and first scientific results based on Guar-

The Messenger 149 – September 2012 55 Astronomical News

ESO 50th Anniversary Activities

A number of products are available as Documentary film is available5. The exhibition catalogue will part of ESO’s 50th anniversary celebra- be available at the venues and may also tions. More details of the 50th anniver- A 63-minute HD blu-ray film is being be downloaded or ordered in hardcopy6. sary activities are available on the web released in conjunction with Europe to page1. the Stars, taking a graphical journey behind the scenes of ESO. The narration Links is in English and subtitles are available 1 50 years of ESO web page: http://www.eso.org/ Books in 20 languages, including some not cov- public/outreach/50years.html ered by ESO member states4. This 2 C. Madsen, The Jewel on the Mountaintop, Wiley- Claus Madsen’s book, The Jewel on the DVD will be distributed with the Decem- Wiley-VCH. Price: €49.90 from http://www.wiley- Mountaintop — The European Southern ber issue of The Messenger. vch.de 3 G. Schilling, L. L. Christensen, Europe to the Stars, Observatory through Fifty Years, has Wiley-VCH. Price: €34.90 from http://www.wiley- been produced especially for ESO’s 50th vch.de anniversary. It contains 560 pages of Exhibition 4 Europe to the Stars — ESO’s first 50 years of ESO history with stories about the people exploring the southern sky (blu-ray DVD) available from http://www.eso.org/public/shop/product/ behind the organisation and 150 historical Awesome Universe is a public exhibition cdrom_europe_stars_bluray/. Price: €5.99, with a photos and illustrations 2. celebrating 50 years of ESO’s exploration reduction for bulk orders. of the southern sky. It is presented in 5 Listing of all the Awesome Universe exhibition ven- An illustrated 264-page coffee-table Europe and around the world. Dozens ues: http://www.eso.org/public/events/special-evt/ awesome-universe/venues.html book, Europe to the Stars, has also been of venues have already hosted this exhi- 6 Awesome Universe exhibition catalogue: http:// released for the 50th anniversary3, re- bition, such as the Museu de Ciencias www.eso.org/public/products/books/eso50_ splendent with 300 of the best hand- Naturais PUC Minas in Brazil and the exhibition_catalogue/ picked images from ESO’s large collec- Sternwarte Reutlingen, Germany, and tion of more than 100 000 images from many more will do so over the next few ESO telescopes. months. A full listing of exhibition venues

56 The Messenger 149 – September 2012 Astronomical News

Fellows at ESO

Myriam Rodrigues And here I am, writing this article from my room at the Paranal Residencia. I started Like many astronomers, I’ve had the my ESO-Chile Fellowship two years ago amazing chance to realise a child’s and I am a support astronomer at Unit dream: “When I grow up, I want to be an Telescopes 1 and 2. I have learnt a lot astronomer!” in these past two years about observation strategies, operations and instrumen- Everything started 20 years ago, when a tation. Being a support astronomer has family friend working in a condensed allowed me to be a more complete astro- matter lab took me into the lab for a cou- physicist by seeing the complete chain ple of days. At the time, condensed mat- of the science. I always find that moment ter physicists were excited by a new toy, when a new frame appears gradually invented a few years earlier: the scanning on the screen fascinating. At this exact tunnelling microscope. I was just seven moment, the incomprehensible light aris- years old, but I still remember perfectly Myriam Rodrigues ing from the sky above our heads is the huge instrument filling the room and a caught in the pixels of the detector and little TV with some kind of purple spheres was no research on distant galaxies at becomes science. on the screen. “These are atoms,” they the astronomy department and I started said, “and these are molecules,” point- to look for a place to do my undergradu- That’s it! This is the story of a stubborn ing to another screen close to another ate research project on galaxy evolution. daydreamer. huge piece of machinery. I came back to I finally decided to send an email directly school, totally convinced that I wanted to François Hammer of the Paris Obser- to be a particle physicist and feeling like a vatory to ask for an undergraduate pro- Rubén Sánchez-Janssen new Messiah preaching new-found truth ject. A few months later, I left the sunny to my schoolmates: “Matter is made skies of Lisbon to start a Masters in When I was a child, I was all about dino- of molecules and molecules are made of astrophysics at the Paris Observatory saurs and outer space. But I guess that, atoms, how cool is that?!” and one year later began a PhD on having grown up in the Canary Islands galaxy evolution in the team of François and with an engineer dad who works on I would have probably become a particle Hammer. infrared astronomical instrumentation, physicist if the star-studded night sky the odds were uneven. I think I made The at my grandmother’s village in Spain had My main research topic is the study of Decision to become an astronomer dur- not brought the poetry of astronomy to the interstellar medium and stellar popu- ing a cold February night in the late 80s, me. On summer nights, the children used lations of intermediate-mass galaxies at after a visit to the IAC80 telescope in to go to the “movie theatre”: a field with a intermediate redshift. This galaxy popu Tenerife with my father. Of course I had clear horizon. Lying on the warm ground, lation appears to be the likeliest progeni- no clue what the job was really about, with a pack of sunflower seeds (the tor of the present-day spiral galaxies and but became absolutely fascinated by the Spanish version of popcorn) in hand, we their properties therefore provide strong quietness of the telescope control room used to gaze at the sky for hours: the constraints on galaxy evolution models. at those after midnight hours. What really Milky Way, shooting stars, the constella- During my PhD I started working on touched me, though, was the image of tions. The link between these two pas- the characterisation of the interstellar a galaxy that the astronomers had just sions fused a few years later, when I dis- medium — metallicity, star formation rate obtained. That whole big collection of covered in a kid’s science book an (SFR), gas fraction and presence of star- stars existed somewhere out there, and incredible invention: spectroscopy! It is formation-driven outflows — of distant they got to observe it in much greater possible to make the atoms of stars and galaxies from integrated spectroscopy detail than I could have ever imagined! nebulae speak! I was definitely decided: from FORS2 on the Very Large Tele- I wanted to study galaxies using spec- scope. I also worked on the estimation of So that was it. I pursued that winter troscopy. Some years ago, I read a quote their stellar populations using broadband night’s dream and years later obtained a from Annie Jump Cannon that remains spectral energy distributions from the degree in Astrophysics at the Universi- carved in my mind. She expressed beau- ultraviolet to the infrared combined with dad de La Laguna. This was followed tifully what had been on my mind all Lick indices and SFR. by a PhD at the Instituto de Astrofísica de those years: “They are not only lines for Canarias on the effects of the environ- me; each new spectrum opens the door I applied for the ESO-Chile Fellowship ment on the evolution of galaxies in to a new wonderland. It is as if the distant moved by the same child’s dream. The nearby clusters. My enchantment with stars have acquired the gift of speech small child in me was categorical: there is telescopes not only persisted, but in- and started to tell us their physical condi- only one place in the world where you creased with the years of experience. tions and constitution.” can be an astronomer. This place is the I was therefore excited when I got the Very Large Telescope at the Paranal opportunity to join ESO as a Fellow in I studied physics at the Instituto Superior Observatory, surrounded by the driest Chile and work at the VLT. I landed in Tecnico at Lisbon. Unfortunately there desert and the darkest sky in the world. Santiago on a cold and rainy day in mid-

The Messenger 149 – September 2012 57 Astronomical News

I look in my rear view mirror and realise voted to the investigation of the proper- my time at ESO has gone by fast. I have ties of young low-mass stars and brown just started the fourth and last year of dwarfs and their circumstellar discs, both my Fellowship, and the future awaits. in our Milky Way and in the Magellanic I still like dinosaurs. But above all, I love Clouds. These studies aim at clarifying my job. the star formation mechanism, its dependency on specific star-forming conditions (such as metallicity, the presence Loredana Spezzi of strong radiation fields, etc.) and, in particular, to identify the specific condi- Thinking back, I was around the age of tions leading to the formation of planets six when I first thought about “knowing in circumstellar discs and to assess how more about stars” (the word “astronomy” frequently they occur. My approach is was not yet part of my vocabulary). mainly observational. I make extensive use of both imaging and spectroscopic I grew up in Sicily and during my child- data from ESO ground-based telescopes Rubén Sánchez-Janssen hood I spent innumerable summer nights and satellite observatories (HST, Spitzer sitting with my father on our terrace, try- and Herschel). August 2009, a mere month after my ing to fight the heat (typically 40 degrees) PhD defence. I had spent my entire life on and enjoying the view of the Milky Way Of course, the ten years I have spent so a small Atlantic island, and was expect- on a clear night in the south of Italy. Dur- far in the astronomy world have given me ing some rough times ahead and a ing those nights I exhausted him with much more than the pleasure of satisfy- period of adjustment. It took me less than the never-ending questions that children ing the whim of a six-year old girl. I have a week to realise that this new place of that age ask about all the inexplica- lost count of the many breathtaking 9 000 kilometres away was easily to be- ble details of this world. One of the more places that I have visited during the sev- come my second home. recursive ones was: “Dad … tell me eral observing trips, conferences, meet- about the Universe!” and “Dad…tell me ings and, even more importantly, I have At ESO I’ve continued my research on more about the Universe!” I repeated it lost count of the many outstanding peo- galaxy evolution as a function of mass over and over again and, after a few sum- ple I have met. Some of them have been and environment, and established new mers, my father (who studied medicine) my mentors, supervisors and advisors, collaborations with colleagues at Vita- had no more news for me and redirected and they have transmitted to me a fund of cura, at other Chilean institutions and me to illustrated astronomy books. The human and professional experiences from abroad. During my functional duties interest stayed with me and the illustrated that will stay with me until the end of my as a Fellow I have supported observa- books became university textbooks, career. Many others are colleagues, tions at the Paranal Observatory, with a when at the age of 19 I decided to study sharing with me the good and the bad of particular commitment to VLT/UT3 and physics, foreseeing a future career in this job. Finally, many of them are people its suite of instruments. More specifically, astrophysics (and not knowing exactly with no connection with astronomy what- I’ve been the VIMOS Fellow during the what was the deal!). soever. I crossed their paths just because recent instrument upgrade project, which I was following mine, but they have has allowed me to become involved in And so the amazing “trip” started: I grad- become immeasurable lifetime friends. the re-commissioning activities together uated in Physics and I obtained a PhD in with a great team of engineers and as- Astrophysics at the University of Catania. tronomers. After that, I had the privilege to be a post- doctoral fellow in two of the top European Paranal is a place that everyone should institutes for astronomy and space sci- visit at least once. You reach the mining ence: first the European Space Agency city of Antofagasta and start travelling (ESA-ESTEC at Noordwijk in the Nether- deeper into the heart of the Atacama lands) and now at ESO-Garching. Desert. One rock, five rocks, 377 rocks, 6765 rocks ... and nothing else but rocks. The “trip” turned out to be long, not And then, out of the blue, the telescopes’ always easy and it is not yet over! I am silhouettes out in the distance, like giants still looking for the “final destination”, in a modern Quixote’s wildest delirium. but in the meanwhile the little six-year old Sunsets from the telescope platform are “me” is quite satisfied. Not only does one of the greatest privileges of observa- she “know a lot about stars”, but she is tory life, when the desert is painted in red even trying to understand how and why and shadows play with hills and moun- they are up there! Translated into the tains. Afterwards, from dusk to dawn, it’s language of an adult astronomer, this the time of the astronomer. means that my current research is de- Loredana Spezzi

58 The Messenger 149 – September 2012 Astronomical News

Personnel Movements

Arrivals (1 July–30 September 2012) Departures (1 July–30 September 2012)

Europe Europe Baltayne Korompay, Katalin (H) Paid Associate Arbogast, Dina (D) Adminstrative Assistant García Dabó, César Enrique (E) Software Engineer Bressert, Eli (USA) Student Gray, Peter Murray (AUS) Project Engineer Daemgen, Sebastian (D) Student McLay, Stewart (GB) Software Engineer Goddi, Ciriaco (I) Fellow Nielsen, Bitten (DK) Student González Gutiérrez, Juan Esteban (RCH) Fellow Heckel, Isabell (D) Adminstrative Assistant Julbe Lopez, Francesco (E) Software Engineer Kempf, Andreas (D) Electronics Engineer Krajnovic, Davor (HR) Fellow Kümmel, Martin (D) Scientific Data Analyst Lagadec, Eric (F) Fellow Moerchen, Margaret (USA) Fellow Kissler-Patig, Markus (D) E-ELT Project Scientist Smiljanic, Rodolfo (BR) Fellow Wieland, Gerd (D) Senior Contract Officer Yaitskova, Nataliya (RUS) Applied Scientist

Chile Chile Alvarez, Nicolas (RCH) Electronics Control Engineer Hills, Richard (GB) ALMA Project Scientist Müller, Andre (D) Fellow Lucas, Robert (F) Astronomer ALMA Commissioning Ober, Claudia (RCH) Contract Officer Manjarrez, Guillermo (MEX) Student Rodriguez, Francisco (RCH) Press Officer Parra, Ricardo Andrés (RCH) Mechanical Engineer Vasquez, Sergio (RCH) Student Rawlings, Mark (GB) Operations Staff Astronomer Vanderbeke, Joachim (B) Student

Construction of the extension to ESO Head- quarters was begun at the beginning of this year and has now reached the second floor, as shown in this recent image. More details of the building concept can be found in a Messenger article (135, p. 2) and in Release eso1215.

The Messenger 149 – September 2012 59 ESO, the European Southern Observa- Contents tory, is the foremost intergovernmental astronomy organisation in Europe. It Telescopes and Instrumentation is supported by 15 countries: Austria, G. Lo Curto et al. – Astronomical Spectrograph Calibration at the Belgium, Brazil, the Czech Republic, Exo-Earth Detection Limit 2 Denmark, France, Finland, Germany, M. Arnaboldi et al. – ESO VISTA Public Surveys — A Status Overview 7 Italy, the Netherlands, Portugal, Spain, D. Bramich et al. – On the Photometric Calibration of FORS2 and the Sweden, Switzerland and the United Sloan Digital Sky Survey 12 Kingdom. ESO’s programme is focused S. Ramsay – Provisional Acceptance of KMOS 16 on the design, construction and opera- M. Kasper et al. – Gearing up the SPHERE 17 tion of powerful ground-based observing facilities. ESO operates three obser- Astronomical Science vatories in Chile: at La Silla, at Paranal, I. Saviane et al. – New Surprises in Old Stellar Clusters 23 site of the Very Large Telescope, and L. Morelli et al. – Stellar Populations of Bulges in Galaxies with at Llano de Chajnantor. ESO is the Low Surface-brightness Discs 28 European partner in the Atacama Large L. Koopmans, O. Czoske – On the Inside of Massive Galaxies: Millimeter/submillimeter Array (ALMA) The Sloan Lens ACS Survey and Combining Gravitational Lensing with under construction at Chajnantor. Stellar Dynamics and Stellar Population Analysis 33 Currently ESO is engaged in the design M. Swinbank et al. – An ALMA Survey of Submillimetre Galaxies in the of the European Extremely Large Extended Chandra Deep Field South: First Results 40 Telescope. T. Nagao et al. – Chemical Properties of a High-z Dusty Star-forming Galaxy from ALMA Cycle 0 Observations 44 The Messenger is published, in hardcopy and electronic form, four times a Astronomical News year: in March, June, September and S. Randall et al. – Report on the ALMA Community Days: Early Science December. ESO produces and distrib- in Cycle 1 47 utes a wide variety of media connected H. Falcke et al. – Report on ESO Workshop “mm-wave VLBI with ALMA and to its activities. For further information, Radio Telescopes around the World” 50 including postal subscription to The J. Walsh – Some Reflections on the SPIE 2012 Symposium on Messenger, contact the ESO education Astronomical Telescopes + Instrumentation 54 and Public Outreach Department at the V. Mainieri – Report on the Symposium “30 Years of Italian Participation following address: to ESO” 55 ESO 50th Anniversary Activities 56 ESO Headquarters Fellows at ESO – M. Rodrigues, R. Sánchez-Janssen, L. Spezzi 57 Karl-Schwarzschild-Straße 2 Personnel Movements 59 85748 Garching bei München Germany Phone +498932006-0 [email protected]

The Messenger: Editor: Jeremy R. Walsh; Design, Layout, Production: Jutta Boxheimer; Layout, Typesetting: Mafalda Martins; Graphics: Roberto Duque www.eso.org/messenger/

Printed by G. Peschke Druckerei GmbH, Front cover: A remarkable early observation by the Atacama Large Millimeter/sub- Schatzbogen 35, 81805 München, millimeter Array (ALMA) taken in Cycle 0 reveals a spiral structure in the molecular Germany material around the asymptotic giant branch (AGB) star R Sculptoris. While shells of cool gas have been detected around AGB stars before, the additional presence Unless otherwise indicated, all images of a spiral feature, detected in CO(J=3-2) emission at 345 GHz with ALMA (Band 7) in The Messenger are courtesy of ESO, interior to the main shell, is revealed for the first time (shown here in the emission except authored contributions which velocity slice around the stellar velocity). The spiral pattern can be explained by a are courtesy of the respective authors. binary companion orbiting the central star with a period of about 350 years and winding up the escape of the wind from the AGB star. This investigation was led by © ESO 2012 Matthias Maercker, ESO Fellow at the ALMA Regional Centre Bonn node, and ISSN 0722-6691 more details can be found in Release 1239.