Telescopes and Instrumentation

4MOST — 4-metre Multi-Object Spectroscopic Telescope

Roelof de Jong1 enough to detect chemical and kinematic metal-poor stars to constrain early gal- substructure in the stellar halo, bulge axy formation and the nature of the first and thin and thick discs of the Milky Way, stellar generations in the Universe. 1 Leibniz -Institut für Astrophysik Potsdam and enough wavelength coverage (> 1.5 (AIP), Germany octave) to secure velocities of extra­ eROSITA (extended ROentgen Survey galactic objects over a large range in red­ with an Imaging Telescope Array, Predehl shift. Such an exceptional instrument et al., 2010) will perform all-sky X-ray sur­ Team members: enables many science goals, but our veys in the years 2013 to 2017 to a limit­ 1 2 2 Svend Bauer , Gurvan Bazin , Ralf Bender , Hans design is especially intended to comple­ ing depth that is a factor 30 deeper than Böhringer3, Corrado Boeche1, Thomas Boller3, Angela Bongiorno3, Piercarlo Bonifacio4, Marcella ment two key all-sky, space-based ob­ the ROSAT all-sky survey, and with Brusa3, Vadim Burwitz3, Elisabetta Caffau5, Art servatories of prime European interest, broader energy coverage, better spectral ­Carlson2, Cristina Chiappini1, Norbert Christlieb5, Gaia and eROSITA. Such a facility has resolution and better spatial resolution 4 6 1 Mathieu Cohen , Gavin Dalton , Harry Enke , been identified as of critical importance in (see Figure 3). We will use 4MOST to ­Carmen Feiz5, Sofia Feltzing7, Patrick François4, Eva Grebel5, Frank Grupp2, Francois Hammer4, Roger a number of recent European strategic ­survey the > 50 000 southern X-ray gal­ Haynes1, Jochen Heidt5, Amina Helmi8, Achim documents (Bode et al., 2008; de Zeeuw axy clusters that will be discovered by Hess2, Ulrich Hopp3, Andreas Kelz1, Andreas Korn9, & Molster, 2007; Drew et al., 2010; Turon eROSITA, measuring 3–30 galaxies in 10 4 10 Mike Irwin , Pascal Jagourel , Dave King , Gabby et al., 2008) and forms the perfect com­ each cluster. These galaxy cluster meas­ Kroes11, Georg Lamer1, Florian Lang-Bardl2, Richard McMahon10, Baptiste Meneux2, Shan Mignot4, Ivan plement to the many all-sky survey pro­ urements determine the evolution of Minchev1, Joe Mohr2, Volker Müller1, Bernard jects around the world. ­galaxy populations in clusters, yield the Muschielok2, Kirpal Nandra3, Ramon Navarro11, cluster mass evolution, and provide 10 11 5 Ian Parry , Johan Pragt , Andreas Quirrenbach , highly competitive constraints on dark William Rambold1, Martin Roth1, Roberto Saglia3, Paola Sartoretti4, Olivier Schnurr1, Axel Schwope1, Science drivers energy evolution. 4MOST enables us to Matthias Steinmetz1, Jesper Storm1, Will Sutherland12, determine the nature of > 1 million active Rikter Horst11, David Terrett6, Ian Tosh6, Scott The Gaia satellite will provide distances galactic nuclei (AGNs), thus constraining 8 11 1 Trager , Lars Venema , Marija Vlajic , Jacob from parallaxes and space kinematics the cosmic evolution of active galaxies Walcher1, Nicolas Walton10, Mary Williams1, Lutz Wisotzki1 from proper motions for more than to z = 5. With 4MOST we will characterise one billion Milky Way stars down to several ­hundreds of thousands of m ~ 20 mag. Gaia will also provide radial dynamo- and accretion-powered Galactic 1 2 V Leibniz-Institut für Astrophysik Potsdam, Univer­ velocities and astrophysical characteri­ X-ray emitters, thereby uncovering the sitäts-Sternwarte Munchen, 3 Max-Planck-Institut für extraterrestrische Physik, Garching, 4 GEPI, Observ­ sation for about 150 million stars, but its active Milky Way and constraining evolu­ 5 atoire de Paris, Zentrum für Astronomie der Univer­ sensitivity is limited to mV ~ 12–16 mag, tionary channels of stellar populations. sität Heidelberg, 6 Rutherford Appleton Laboratory, strongly dependent on stellar spectral 7 8 Didcot, Lund Observatory, Kapteyn Astronomical type, because its spectrograph only cov­ Other science cases that are fully feasible Institute, Groningen, 9 Department of Physics and Astronomy, Uppsala University, 10 Institute of Astron­ ers the Ca ii-triplet region at 847–874 nm. with 4MOST, but that will not drive the omy, Cambridge, 11 NOVA-ASTRON, the Nether­ Figure 1 shows how, by covering the design, include the dynamic structure lands, 12 Queen Mary College London. full optical wavelength region, the 4MOST and content of nearby galaxies, follow-up instrument complements Gaia where it of extragalactic radio and infrared sur­ lacks spectroscopic capabilities, so that veys, and constraining dark energy prop­ 4MOST (4-metre Multi-Object Spectro- full 6D-space coordinate information erties through baryon acoustic oscillation scopic Telescope) is a very large field can be obtained and objects throughout (BAO) measurements. (goal > 5 square degrees) multi-object the Milky Way chemically characterised. spectrograph with up to 3000 fibres Large-area surveys of faint Galactic and spectral resolutions of 5000 and ­stellar objects will enable us to elucidate Instrument specification 20 000, proposed for the New Technol- the formation history of the Milky Way. ogy Telescope (NTT) or the VISTA sur- The 4MOST facility consists of a wide- vey telescope. The science cases cov- Models of hierarchical galaxy formation field corrector with atmospheric disper­ ering Gaia follow-up for chemistry and predict large amounts of dynamical sion corrector, acquisition, guiding kinematics of the Galaxy and redshift ­substructure in the Milky Way halo that and wavefront sensing systems, a fibre- surveys of targets from the eROSITA 4MOST can detect through measuring positioning system, and a fibre train X-ray mission are briefly outlined. red giant branch (RGB) stars (see Fig­ ­feeding the light to an R > 20 000 spectro­ ure 2). Furthermore, we will determine graph and several R ~ 5000 spectro­ the three-dimensional Galactic potential graphs. The baseline and goal instrument The 4MOST consortium aims to pro- and its substructure, discern the dynami­ specifications can be found in Table 1. vide the ESO community with a fibre-fed cal structure of the Milky Way disc and We have preliminary wide-field corrector spectroscopic survey facility on either measure the influence of its bar and designs yielding 7 square degree FoV VISTA or the NTT with a large enough spiral arms, measure the Galactic assem­ on the VISTA 4.1-metre telescope and field of view (FoV) to survey a large frac­ bly history through chemo-dynamical 3 square degree FoV on the 3.58-metre tion of the southern sky in a few years, a substructure and abundance pattern NTT. We will study two fibre positioner multiplex and spectral resolution high labelling, and find thousands of extremely designs, one based on a variation of

14 The Messenger 145 – September 2011 Effective temperature (K) Gaia predicted 14 30 000 10 000 7000 6000 4000 B0V –10 Limiting distance A0V –8 12 F0V Supergiants (I) AGB –6 1 Mpc G5V K4V –4 10 M star 10 ☉ Helium K1III –2 flash and) 5 M star ☉ 100 kpc –b s)

V 0 II III 8 ( Giants ( , ) HB 10 Main sequence kpc km/ (

R 2

V RGB gnitud σ

4 (V 10 kpc 6 ma )

te Sun 1 kp 6 c solu

4 Ab 8 Whit RGB - Red Giant Branch 1 kpc 10 e dw HB - Horizontal Branch 100 pc ar Gaia 2 12 fs AGB - Asymptotic Giant Branch (W 4MOST goal D) 14 100 pc 0 4M0ST 8 10 12 14 16 18 20 22 05 B5 A0 F0 G0 K0 M0 V mag Spectral class

Figure 1. Left: The 4MOST goal for radial velocity thereby enabling 6D-phase space studies to Gaia’s to nearly the centre of the Milky Way, RGB stars to accuracy compared to the Gaia end of mission limits. Right. Limiting distances for radial velocity 100 kpc, and massive stars throughout the Local accuracy as function of stellar apparent magnitude. measurements with Gaia (maroon diagonal) and Group, substantially expanding on Gaia’s spectro­ Our aim is to match the spectroscopic magnitude 4MOST (black horizontal) overlaid on a Hertzsprung– scopic view. Distance limits for the 4MOST high res­ limits of 4MOST to the astrometric limits of Gaia, Russell diagram. 4MOST can measure Sun-like stars olution spectroscopy are about four times smaller. the Echidna design as developed by the Efficient full-sky surveying requires at of R ~ 5000 covering the full optical ­Australian Astronomical Observatory least 1500 targets to be observed simul­ wavelength range, but about 10% of the (AAO) for FMOS (Akiyama et al., 2008) taneously, but our goal is to provide a fibres will permanently go to a spectro­ and another one based on the positioner multiplex of > 3000 to create a unique, graph with resolution of R > 20 000. The design of the Guoshoujing (formerly world-class facility. Most fibres will lead facility will be complemented with a LAMOST) Telescope (Hu et al., 2004). to spectrographs with spectral resolution full array of software to enable target se­ lection, scheduling, data reduction and ­analysis, and an archive. During the Figure 2. Spatial and radial velocity substructure dis­ halo in four distance bins (left) and in one direction ­conceptual design phase we will perform tribution of RGB stars on the sky for a stellar halo on the sky (right) and clearly demonstrates the large a number of trade-off studies to find the formed in the Aquarius project cosmological simula­ amount of substructure that becomes apparent, tions (Cooper et al., 2010; Helmi et al., 2011). The consequent on the opening of a new phase-space projection corresponds to stars located in the inner dimension (in this case, line-of-sight velocity).

–500 400

200 s) km/ y (

[0,15] kpc [15,30] kpc locit 0

0 ve

Radial –200

–400

b = [–30,0], I = [–100, –60] deg 500 [30,45] kpc [45,60] kpc km/s 0 10 20 30 40 50 60 Distance from the Sun [kpc]

The Messenger 145 – September 2011 15 Telescopes and Instrumentation de Jong R. et al., 4MOST

European astronomers would not have direct access to them. For many science cases where spectral samples of more than a few 100 objects are re­­quired, 4MOST will outperform existing instru­ mentation on 8-metre-class telescopes like FLAMES and VIMOS. Running in ­permanent Public Survey mode, it will take observations for many science pro­ grammes simultaneously, enabled by its huge grasp in multiplex, field of view and wavelength coverage. The reduced photon-gathering power of a 4-metre- class telescope is thus easily compen­ sated by the larger field of view and the increased time available per target. Therefore, if 4MOST is realised, the ESO community gains a facility that can 0.10.2 0.40.9 1.9 4.18.6 18 38 cluster number density (deg–2) be described as an 8-metre-class instru­ ment on a 4-metre telescope. Figure 3. All-sky map (in Aitoff projection) of the pre­ The consortium will make all data, includ­ dicted number density of eROSITA galaxy cluster ing high-level science products, available detections (from Mühlegger, 2010). 4MOST enables References efficient follow-up of the ~70 000 clusters detected to the general public in yearly increments in the southern hemisphere and provides dynamical through a high-quality database system. Akiyama, M. et al. 2008, SPIE, 7018, 94 mass estimates for a large fraction of them by meas­ Bode, M., Cruz, M. & Molster, F. 2008, The uring radial velocities of 5–30 galaxies in each cluster. European astronomers have currently ASTRONET Infrastructure Roadmap no access to a 4MOST-like facility, and Cooper, A. P. et al. 2010, MNRAS, 406, 744 optimal designs for both the VISTA and frankly, such an instrument does not de Zeeuw, P. & Molster, F. 2007, A Science Vision for European Astronomy (ASTRONET) the NTT telescopes, with ESO then mak­ exist worldwide. Only the HERMES Drew, J. et al. 2010, Report by the European ing the final telescope selection about instrument currently under construction telescope strategic review committee on Europe’s halfway through the study. for the AAO in combination with the 2–4m telescopes over the decade to 2020 planned, but not yet funded, BigBOSS or (ASTRONET) Helmi, A. et al. 2011, ApJL, 733, L7 SuMIRe prime focus instruments (for Hu, H. et al. 2004, SPIE, 5492, 574 Surveys with 4MOST the 4-metre Kitt Peak and 8-metre Sub­ Mühlegger, M. 2010, Ph.D. thesis, Technische aru telescopes respectively) would pro­ Universität München To reach maximum impact, we propose vide similar capabilities as those pro­ Predehl, P. et al. 2010, SPIE, 7732, 23 Turon, C. et al. 2008, Report by the ESA-ESO to use 4MOST continuously for a five-year posed for 4MOST. However, even if these Working Group on Galactic populations, chemis- Public Survey delivering ≥ 7 million (goal instruments were successfully ­constructed, try and dynamics, ST-ECF, ESO 25 million) spectra over 10 000–20 000 square degrees, which is an order of magnitude larger than the Sloan Digital Specification Baseline Goal Sky Survey (SDSS) spectroscopic survey Field of view 3 degree2 > 5 degree2 at > 2.5 times the spectral resolution. Multiplex fibre positioner 1500 > 3000 The targets selected for this Public Sur­ Spectrographs – blue arm vey could be determined through a com­ resolution @ 500 nm R ~ 3000 R ~ 5000 bination of open calls to the ESO astro­ passband 420–650 nm 370–650 nm nomical community and the consortium Spectrographs – red arm guaranteed time observations (GTO), with resolution @ 850 nm R ~ 5000 R ~ 7500 all surveys running in parallel. Ob­­serving passband 650–900 nm 650–1000 nm objects from many survey catalogues HR spectrograph (10–20% of all fibres) simultaneously at each pointing enables resolution R > 20000, surveys that require tens of thousands passbands 390–450 & 585–675 nm objects spread sparsely over the sky. Number of fibres in 2; circle > 3 > 7 Such surveys have too few targets to use Reconfigure time < 8 min < 4 min all 4MOST fibres in one pointing, but are Area (5-year survey) 10000 deg2 2 × ~ 20 000 deg2 too large to be performed in standard Objects (5-year survey) 6 × 106 > 20 × 106 observing modes with existing facilities. Start operations end 2017

Table 1. Baseline and goal instrument specification.

16 The Messenger 145 – September 2011