Spitzer Space Telescope - General Observer Proposal #3473 Deep infrared imaging around ultraluminous high-redshift galaxies Principal Investigator: Andrew Blain Institution: Caltech Co-Investigators: Scott Chapman, Caltech Ian Smail, University of Durham Lee Armus, Caltech/SSC David Frayer, Caltech/SSC David Alexander, University of Cambridge Rob Ivison, UKATC Science Category: high-z galaxies (z>0.5) Observing Modes: IracMap MipsPhot Hours Approved: 13.5 Abstract: We have compiled a large sample of high-redshift submillimeter-selected galaxies with accurate positions and redshifts in seven well-studied fields around the sky. We propose to obtain fully-sampled MIPS and IRAC images of the regions surrounding these galaxies in three fields where no deep GTO observations are planned, to obtain accurate restframe near-/mid-/far-infrared(IR) luminosities and spectral energy distributions (SEDs) for this unique sample of very luminous distant galaxies. The observations will provide unprecedented information on the luminosities of evolved stellar populations in these galaxies, and seek mid-IR SED measurements that could discriminate between star formation and AGN activity during the most active epoch of galaxy formation in the distant Universe. These observations will allow us to test whether the tight correlation between the far-IR and radio emission seen in local star-forming galaxies holds at much earlier times, out to redshifts of order 3, by measuring accurate restframe SEDs for these dusty galaxies whose redshifts we know. In addition, these observations will provide constraints on the mid-IR properties of other, less active, galaxies in large scale structures we have identified around the submm sources where we have a rich redshift catalog.