Geach, J. E. and Smail, Ian and Ellis, R. S. and Moran, S. M. and Smith, G. P. and Treu, T. and Kneib, J.-P. and Edge, A. C. and Kodama, T. (2006) A panoramic mid-infrared survey of two distant clusters. Astrophysical Journal, 649 (2). pp. 661-672. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:GEAapj06
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We present panoramic Spitzer MIPS 24 μm observations, covering ~9 × 9 Mpc^2 (25' × 25') fields around two massive clusters, Cl 0024+16 and MS 0451-03, at z = 0.39 and z = 0.55, respectively, reaching a 5 σ flux limit of ~200 μJy. Our observations cover a very wide range of environments within these clusters, from high-density regions around the cores out to the turnaround radius. Cross-correlating the mid-infrared catalogs with deep optical and near-infrared imaging of these fields, we investigate the optical/near-infrared colors of the mid-infrared sources. We find excesses of mid-infrared sources with the optical/near-infrared colors expected of cluster members in the two clusters and test this selection using spectroscopically confirmed 24 μm members. The much more significant excess is associated with Cl 0024+16, whereas MS 0451-03 has comparatively few mid-infrared sources. The mid-infrared galaxy population in Cl 0024+16 appears to be associated with dusty star-forming galaxies (typically redder than the general cluster population by up to A_V ~ 1-2 mag) rather than emission from dusty tori around active galactic nuclei in early-type hosts. We compare the star formation rates derived from the total infrared (8-1000 μm) luminosities for the mid-infrared sources in Cl 0024+16 with those estimated from a published Hα survey, finding rates ≳ 5 times those found from Hα, indicating significant obscured activity in the cluster population. Compared to previous mid-infrared surveys of clusters from z ~ 0-0.5, we find evidence for strong evolution of the level of dust-obscured star formation in dense environments to z = 0.5, analogous to the rise in the fraction of optically selected star-forming galaxies seen in clusters and the field out to similar redshifts. However, there are clearly significant cluster-to-cluster variations in the populations of mid-infrared sources, probably reflecting differences in the intracluster media and recent dynamical evolution of these systems.
|Additional Information:||© 2006 The American Astronomical Society. Received 2006 January 24; accepted 2006 June 5. We thank the anonymous referee, whose comments greatly improved the clarity of this paper. This study is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. This work also made use of the Spitzer Archive, which is operated by the Spitzer Science Center. J. E. G. is supported by a UK Particle Physics and Astronomy Research Council studentship; I. R. S. and G. P. S. acknowledge support from the Royal Society.|
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|Deposited By:||Tony Diaz|
|Deposited On:||09 Jul 2009 21:45|
|Last Modified:||26 Dec 2012 10:54|
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