Identification of a Complete 160 micron 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
micron-selected sources from Spitzer observations of the 1-deg^2 ISO Deep Field
region in the Lockman Hole. 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 micron and 170 micron, has been
used to calculate accurate total infrared luminosities, LIR(8-1000 micron), 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_Sun)=12.74. Over the luminosity range
log(L_IR/L_Sun)=10-12, the LF for LIRGs in the Lockman Hole Deep Field is
similar to that found previously for local sources at similar infrared
luminosities. The mean host galaxy mass, log(M/M_Sun)=10.7, and dominance of
HII-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 LIR. However for the most luminous
sources, log(L_IR/L_Sun)>12.0, we find evidence for strong evolution in the LF
\propto (1+z)6\pm1, assuming pure number density evolution. These ultraluminous
infrared galaxies (ULIRGs) have a larger mean host mass, log(M/M_Sun)=11.0, and
exhibit disturbed morphologies consistent with strong-interactions/mergers, and
they are also more likely to be characterized by starburst-AGN composite or AGN
spectral types.
