Telescopes and Instrumentation Hawk-I – First Results from Science Verification Markus Kissler-Patig1 of the instrument. Here we briefly de- were obtained, for a grand total of 27 Andrea Fontana 2 scribe a selection among the twelve ac- hours of integration. The final mosaic pro- Bram Venemans 3 cepted Science Verification programmes vides the deepest image ever obtained Jean-Paul Kneib 4 and highlight some of the first spectac- in the Y-band. Thanks also to the excel- Michelle Doherty1 ular results in the areas of distant galax- lent image quality (< 0.5), it enables the Christopher Lidman1 ies, clusters of galaxies, star clusters and detection of galaxies as faint as m(AB) Harald Kuntschner 5 star formation. = 26.8. The preliminary photometric anal- Mark Norris 6 ysis has identified a set of 25 high-red- Soeren Larsen7 The science verification (SV) for HAWK-I shift candidates. Extensive simulations Mark Gieles1 was interleaved with the commissioning are underway to assess the complete- Alcione Mora Fernandes 8 activities that took place in three runs ness and reliability of the selected sam- Mark McCaughrean 9 between October 2007 and February ple. Thomas Preibisch10 2008. The goal of SV was to demonstrate Andreas Seifahrt11 the capabilities of the new instrument This programme was complemented by Jon Willis12 in a wide variety of research fields. More HAWK-I observations in the NB1060 filter Elizabeth Wehner13 details on SV, the selected programmes as an alternative method to search for and all the data, together with a de- star-forming galaxies at z = 7.7, thus dem- scription of how they were acquired, can onstrating the potential of HAWK-I in di- 1 ESO be found on the HAWK-I SV web pages rectly probing the epoch of re-ionisation. 2 INAF – Osservatorio Astronomico di (http://www.eso.org/sci/activities/vltsv/ The SV observations alone will form a Roma, Italy hawkisv/). HAWK-I was offered to the sufficiently complete dataset to put a con- 3 Institute of Astronomy, University of community in Period 81 for regular serv- straint on the number of luminous star- Cambridge, United Kingdom ice and visitor mode observing. forming galaxies at z = 7.7. Preliminary 4 OAMP, Laboratoire d’Astrophysique de analysis of 8.3 hours of narrowband data Marseille, France indicates that HAWK-I is capable of 5 ST-ECF, ESO Distant galaxies reaching a limiting depth of 7.5 × 10–18 erg 6 Department of Physics, University of s –1 cm–2 arcsec–2 (5 sigma). By measur- Durham, United Kingdom HAWK-I observations in the GOODS-S ing the colours of the candidate line emit- 7 Astronomical Institute, University of field were designed to obtain a self-con- ters in the available HST/ACS images of Utrecht, the Netherlands sistent sample of galaxies at redshift the field, the line which has caused the 8 Departamento de Física Teórica C-XI, about 7, providing a new view on the Uni- narrowband excess can be determined. Universidad Autónoma de Madrid, verse at the end of the epoch of re-ioni- Figure 1 shows a colour-magnitude dia- Spain sation. The extraordinary efficiency of gram of detected sources and an exam- 9 School of Physics, University of Exeter, HAWK-I was used to detect z > 6.5 can- ple image of a low-redshift emission-line United Kingdom didates in the Y-filter (centred at 1.021 µm) galaxy. 10 Max-Planck-Institut für Radioastro- through an appropriate recasting of nomie, Bonn, Germany the Lyman-break technique: candidates A programme with similar aims, but using 11 Institut für Astrophysik, Georg-August- are selected as “Z-drop”, i.e. their col- a different technique, aimed at detecting Universität, Göttingen, Germany ours satisfy the following criteria: (Z–Y) > high-redshift (z ~ 7.7) Ly-A emitters am- 12 Department of Physics and Astronomy, 1.0 mag. and (Y–K) < 1.5 mag. 333 frames plified by the strong lensing of a massive University of Victoria, Canada 13 Department of Physics and Astronomy, McMaster University, Hamilton, Canada B VI Z Sigma = 3 2 The VLT wide-field near-infrared imager Z = 0.69 –> L(H) = 8 × 10 40 erg/s HAWK-I was commissioned in 2007 and ) phot B 1 A Science Verification (SV) programmes ( Figure 1. Colour-magni- 0 Equivalent Width = 100 A were conducted in August 2007. A selec- 6 tude diagram showing 0 tion of results from among the twelve 1 objects detected in one B N Science Verfication proposals are sum- of the four HAWK-I – 0 chips. Candidate emis- marised. Y sion-line galaxies are objects with a significant flux excess in the nar- HAWK-I is the new wide-field infrared im- row-band filter. The inset ager on the VLT. We reported previously –1 shows ACS images of in The Messenger on its capabilities an example low-redshift line emitter, detected (Casali et al., 2005) and refer to Kissler- 14 16 18 20 22 24 26 through HA redshifted to Patig et al. (2008) for a recent description NB1060 magnitude (AB) z = 0.69. The Messenger 132 – June 2008 7 Telescopes and Instrumentation Kissler-Patig M. et al., Hawk-I – First Results from Science Verification cluster. The massive cluster MS0451-03 Figure 2. A ~ 2.5 × 2 section of a was observed with the NB1060 filter of HAWK-I Ks-band image contain- ing the radio galaxy MRC0030-219, HAWK-I. The magnification of background which is marked with an arrow. galaxies ranges from 0.3 to 3 mag. The NB image provides an effective test for the presence of gravitationally lensed z ~ 7.7 galaxies. Many interloping z < 7 galaxies are detected in this image and will be of wider interest for follow-up studies. Galaxy clusters There is now strong evidence that galaxy evolution is closely linked to environment Figure 3. Colour composite of four and that the oldest, reddest galaxies lo- HAWK-I pointings in both J and Ks, covering 13.5 on a side, of the gal- cally are found in large clusters. Hence to axy cluster XMMU J2235.3-2557. The study the early stages of galaxy evolution cluster is in the middle of the frame we need to study the highest redshift and a blow-up centred on the cluster (proto-)clusters. The number of these cur- is shown in the inset. The centre of XMMU J2235.3-2557 is dominated by rently known is small but one of the most red galaxies with very similar colours. promising ways to locate them is by char- acterising the environment of high-red- shift radio galaxies which lie at the cen- tres of proto-clusters. HAWK-I was used to image the radio galaxy MRC0030-219 at z = 2.168 in the J-, K- and NB1190-fil- ters (see Figure 2 for the K-band image). At this redshift the narrowband filter traces [O II] 3727 Å emission: the aim is to search for an overdensity of star-forming galaxies and at the same time for redder, evolved galaxies using J–K colours. Initial ages, the image quality reached 0.2, ing. Overplotted are Maraston et al. analysis seems to indicate no evidence which approaches that obtainable with (2003) SSP models for ages 3–15 Gyr for an over-density but this is still to be NICMOS on HST, but with the advantage and [Z/H] –2.25 to 0.67. The depth of the verified. If true, it will allow interesting lim- of a much larger field of view. HAWK-I data allows exploration of the its to be placed on the properties of a interesting blue end (intermediate ages?) radio galaxy required for a forming proto- of the colour distribution in V–Ks. cluster. Star clusters In a similar programme HAWK-I was used A ubiquitous feature in rich galaxy clus- Globular clusters provide important tools to study the star cluster system of the ters at all redshifts is the tight sequence to distinguish between competing models intermediate-age (~ 3 Gyr) merger rem- of red, passively-evolving early-type gal- for the formation of their host galaxies. nant NGC 1316. This galaxy has a sub- axies in the colour-magnitude diagram. The combination of optical and IR pho- stantial number of star clusters, some of HAWK-I is well suited for studying the for- tometry is a very powerful tool to investi- which have ages corresponding to the mation of the red sequence and of rich gate the age distribution of globular clus- merger. However, it is not clear what frac- galaxy clusters in general, since such ters in a given system. However, currently tion were formed during this most recent clusters form over regions that are several available samples are severely limited by merger event. The new, deep Ks-band Mpc in size. In the concordance cosmol- the spatial coverage of the IR data. With imaging (Figure 5) has already revealed ogy, 5 Mpc corresponds to 10 on the HAWK-I, wide field J-, H-, Ks-band imag- an extensive system of star clusters and, sky at a redshift of 1.5. The aim of this SV ing was obtained of the nearest S0 gal- along with archival VIMOS optical imag- programme was to image the galaxy axy NGC 3115. A preliminary colour-col- ing and spectroscopy, will allow the var- cluster XMMU J2235.3-2557 at z = 1.39, our plot, obtained using archival FORS2 ious cluster populations in NGC 1316 to one of the most distant X-ray luminous imaging and the HAWK-I SV data (filled be clearly separated and their ages and clusters known.