An AzTEC 1.1-mm survey for ULIRGs in the field of the Galaxy Cluster MS 0451.6−0305

J. L. Wardlow 3 Ian Smail 1 G. W. Wilson 0 M. S. Yun 0 K. E. K. Coppin 1 R. Cybulski 0 J. E. Geach 3 R. J. Ivison 6 7 I. Aretxaga 5 J. E. Austermann 4 A. C. Edge 1 G. G. Fazio 9 J. Huang 9 D. H. Hughes 5 T. Kodama 8 Y. Kang 2 S. Kim 2 P. D. Mauskopf 11 T. A. Perera 12 K. S. Scott 0 10 0 Department of Astronomy, University of Massachusetts , Amherst, MA 01003, USA 1 Institute for Computational Cosmology, Durham University , South Road, Durham DH1 3LE 2 Astronomy & Space Science Department, Sejong University , Seoul, South Korea 3 Department of Physics, Durham University , South Road, Durham DH1 3LE 4 Center for Astrophysics and Space Astronomy, University of Colorado , Boulder, CO 80309, USA 5 Instituto Nacional de Astrofsica , O ptica y Electronica, Tonantzintla, Puebla, Mexico 6 UK Astronomy Technology Centre, Royal Observatory , Blackford Hill, Edinburgh EH9 3HJ 7 Scottish Universities Physics Alliance, Institute for Astronomy, University of Edinburgh , Blackford Hill, Edinburgh EH9 3HJ 8 National Astronomical Observatory of Japan , Mitaka, Tokyo 181-8588, Japan 9 Harvard-Smithsonian Center for Astrophysics , 60 Garden St. MS-65, Cambridge, MA 02138-1516, USA 10 Department of Physics and Astronomy, University of Pennsylvania , Philadelphia, PA 19104, USA 11 School of Physics & Astronomy, Cardiff University , Queens Buildings, The Parade, Cardiff CF24 3AA 12 Illinois Wesleyan University , P.O. Box 2900, Bloomington, IL 61702-2900, USA A B S T R A C T We have undertaken a deep ( 1.1 mJy) 1.1-mm survey of the z = 0.54 cluster MS 0451.60305 using the AzTEC camera on the James Clerk Maxwell Telescope. We detect 36 sources with signal-to-noise ratio (S/N) 3.5 in the central 0.10 deg2 and present the AzTEC map, catalogue and number counts. We identify counterparts to 18 sources (50 per cent) using radio, mid-infrared, Spitzer InfraRed Array Camera (IRAC) and Submillimetre Array data. Optical, near- and mid-infrared spectral energy distributions are compiled for the 14 of these galaxies with detectable counterparts, which are expected to contain all likely cluster members. We then use photometric redshifts and colour selection to separate background galaxies from potential cluster members and test the reliability of this technique using archival observations of submillimetre galaxies. We find two potential MS 045103 members, which, if they are both cluster galaxies, have a total star formation rate (SFR) of 100 M yr1 - a significant fraction of the combined SFR of all the other galaxies in MS 045103. We also examine the stacked rest-frame mid-infrared, millimetre and radio emission of cluster members below our AzTEC detection limit, and find that the SFRs of mid-IR-selected galaxies in the cluster and redshift-matched field populations are comparable. In contrast, the average SFR of the morphologically classified late-type cluster population is nearly three times less than the corresponding redshift-matched field galaxies. This suggests that these galaxies may be in the process of being transformed on the red sequence by the cluster environment. Our survey demonstrates that although the environment of MS 045103 appears to suppress star formation in late-type galaxies, it can support active, dust-obscured mid-IR galaxies and potentially millimetre-detected LIRGs. 1 I N T R O D U C T I O N Galaxy clusters are highly biased environments in which galaxies potentially evolve more rapidly than in the field. The galaxy populations of local massive clusters contain mainly early-type galaxies which define a colourmagnitude relation (CMR) (Visvanathan & Sandage 1977; Bower, Lucey & Ellis 1992). However, studies of clusters out to z 1 suggest that they contain increasing activity at higher redshifts due to a growing fraction of blue, star-forming galaxies (Butcher & Oemler 1984). Over the same redshift range there appears to be a growing deficit in the CMR population at faint magnitudes, as well as a claimed increasing decline in the numbers of S0 galaxies, suggesting that the blue, star-forming galaxies may be transforming into these passive populations with time (Dressler et al. 1997; Smail et al. 1998; De Lucia et al. 2007; Stott et al. 2007; Holden et al. 2009). The blue, star-forming populations within the clusters are accreted from the surrounding field as the clusters grow via gravitational collapse. The evolution in the star-forming fraction in the clusters may thus simply track the increasing activity in the field population at higher redshifts. The increasing activity in the field is also reflected in an increasing number of the most luminous (and dusty) starburst galaxies with redshift (e.g. Le Floch et al. 2005): the Luminous Infrared Galaxies (with LFIR 1011 L ) and their Ultraluminous cousins (ULIRGs; LFIR 1012 L ). These systems will also be accreted into the cluster environment along with their less-obscured and less-active population as the clusters grow. Indeed, mid-infrared (mid-IR) surveys of clusters have identified a population of dusty starbursts whose activity increases with redshift (e.g. Geach et al. 2006, 2008). However, these mid-IR surveys can miss the most obscured (and potentially most active) galaxies which are optically thick in the rest-frame mid-IR. If they are present in clusters even in relatively low numbers such active galaxies will contribute significantly to the star formation rate (SFR) in these environments and the metal enrichment of the intracluster medium. Hence, to obtain a complete census of the star formation within clusters we need to survey these systems at even longer wavelengths, in the rest-frame far-IR, corresponding to the observed submillimetre and millimetre waveband. Over the past decade or more, there have been a number of studies of rich clusters of galaxies in the submillimetre and millimetre wavebands (e.g. Smail, Ivison & Blain 1997; Zemcov et al. 2007; Knudsen, van der Werf & Kneib 2008). Many of these studies were seeking to exploit the clusters as gravitational telescopes to aid in the study of the distant submillimetre galaxy (SMG) population behind the clusters, while others focused on the detection of the SunyaevZeldovich (SZ) emission. Due to the limitations of current technologies direct detection of millimetre sources is restricted to those with fluxes S1100 m 1 mJy, or equivalently galaxies with SFRs 300 M yr1 much higher than expected for the general cluster populations based on optical surveys. Nevertheless, these studies have serendipitously detected a number of cluster galaxies, although these are either atypical (e.g. central cluster galaxies; Edge et al. 1999) or not confirmed members (e.g. Best 2002; Webb et al. 2005). More critically, with few exceptions these studies have all focused on the central 23 arcmin of the clusters, where the SZ emission and lensing amplification both peak, and have not surveyed the wider environment of the cluster outskirts where much of the obscured star formati (...truncated)