IDENTIFICATION OF A COMPLETE 160 μm FLUX-LIMITED SAMPLE OF INFRARED GALAXIES IN THE ISO LOCKMAN HOLE 1 deg 2 DEEP FIELDS: SOURCE PROPERTIES AND EVIDENCE FOR STRONG EVOLUTION IN THE FIR LUMINOSITY FUNCTION FOR ULIRGs

We have identified a complete, flux-limited (S_(160) > 120 mJy) sample of 160 μm selected sources from Spitzer observations of the 1 deg^2 Infrared Space Observatory (ISO) Deep Field region in the Lockman Hole (LH). Ground-based UV, optical, and near-infrared (NIR) photometry and optical spectroscopy have been used to determine colors, redshifts, and masses for the complete sample of 40 galaxies. Spitzer-IRAC+MIPS photometry, supplemented by ISOPHOT data at 90 μm and 170 μm, has been used to calculate accurate total infrared luminosities, L_(IR)(8-1000 μm), and to determine the IR luminosity function (LF) of luminous infrared galaxies (LIRGs). The maximum observed redshift is z ~ 0.80 and the maximum total infrared luminosity is log (L_(IR)/L_⊙) = 12.74. Over the luminosity range log (L_(IR)/L_⊙)) = 10-12, the LF for LIRGs in the LH Deep Field is similar to that found previously for local sources at similar infrared luminosities. The mean host galaxy mass, log (M/M_⊙ ) = 10.7, and dominance of H_(II)-region spectral types, is also similar to what has been found for local LIRGs, suggesting that intense starbursts likely power the bulk of the infrared luminosity for sources in this range of L_(IR). However for the most luminous sources, log (L_(IR)/L_⊙ ) > 12.0, we find evidence for strong evolution in the LF ∝ (1 + z)^(6±1), assuming pure number density evolution. These ultraluminous infrared galaxies (ULIRGs) have a larger mean host mass, log (M/M_⊙) = 11.0, and exhibit disturbed morphologies consistent with strong interactions/mergers, and they are also more likely to be characterized by starburst-active galactic nucleus (AGN) composite or AGN spectral types.