A Multiwavelength Study of a Sample of 70 micron Selected Galaxies in
  the COSMOS Field I: Spectral Energy Distributions and Luminosities
  We present a large robust sample of 1503 reliable and unconfused 70microm
selected sources from the multiwavelength data set of the Cosmic Evolution
Survey (COSMOS). Using the Spitzer IRAC and MIPS photometry, we estimate the
total infrared luminosity, L_IR (8--1000 microns), by finding the best fit
template from several different template libraries. The long wavelength 70 and
160 micron data allow us to obtain a reliable estimate of L_IR, accurate to
within 0.2 and 0.05 dex, respectively. The 70 micron data point enables a
significant improvement over the luminosity estimates possible with only a 24
micron detection. The full sample spans a wide range in L_IR, L_IR ~ 10^8-10^14
L_sun, with a median luminosity of 10^11.4 L_sun. We identify a total of 687
luminous, 303 ultraluminous, and 31 hyperluminous infrared galaxies (LIRGs,
ULIRGs, and HyLIRGs) over the redshift range 0.01<z<3.5 with a median redshift
of 0.5. Presented here are the full spectral energy distributions for each of
the sources compiled from the extensive multiwavelength data set from the
ultraviolet (UV) to the far-infrared (FIR). Using SED fits we find possible
evidence for a subset of cooler ultraluminous objects than observed locally.
However, until direct observations at longer wavelengths are obtained, the peak
of emission and the dust temperature cannot be well constrained. We use these
SEDs, along with the deep radio and X-ray coverage of the field, to identify a
large sample of candidate active galactic nuclei (AGN). We find that the
fraction of AGN increases strongly with L_IR, as it does in the local universe,
and that nearly 70% of ULIRGs and all HyLIRGs likely host a powerful AGN.
