MIPS Class Coaddition of SWIRE High-Redshift Galaxies

The SWIRE survey encompasses the largest volume of the Spitzer extragalactic surveys, providing the best sensitivity for the detection of significant numbers of rare objects, including the most massive ULIRGs, and obscured AGN. These objects are detected and classified using Spitzer IRAC and MIPS-24 data, but are too faint to be detected individually in the 70 μm and 160 μm bands. We have applied a class coaddition technique to investigate far-infrared spectral energy distributions of these sources by redshift and spectral shape. The variation of far-IR-to-mid-IR colors of the ULIRGs with redshift generally tracks the predictions of template galaxies, and favors the lower-luminosity templates.