Spectral Energy Distributions of Local Luminous and Ultraluminous Infrared Galaxies

Luminous (LIRGs; log (L _IR/L _⊙) = 11.00-11.99) and ultraluminous infrared galaxies (ULIRGs; log (L _IR/L _⊙) = 12.00-12.99) are the most extreme star-forming galaxies in the universe. The local (U)LIRGs provide a unique opportunity to study their multi-wavelength properties in detail for comparison with their more numerous counterparts at high redshifts. We present common large aperture photometry at radio through X-ray wavelengths and spectral energy distributions (SEDs) for a sample of 53 nearby (z < 0.083) LIRGs and 11 ULIRGs spanning log (L _IR/L _⊙) = 11.14-12.57 from the flux-limited (f _{60 μm} > 5.24 Jy) Great Observatories All-sky LIRG Survey. The SEDs for all objects are similar in that they show a broad, thermal stellar peak (~0.3-2 μm), and a dominant FIR (~40-200 μm) thermal dust peak, where νL _ν(60 μm)/νL _ν(V) increases from ~2 to 30 with increasing L _IR. When normalized at IRAS 60 μm, the largest range in the luminosity ratio, R(λ) ≡ log[νL _ν(λ)/νL _ν(60 μm)], observed over the full sample is seen in the hard X-rays (HX = 2-10 keV), where ΔR _HX = 3.73 (\bar{R}_{HX} = -3.10). A small range is found in the radio (1.4 GHz), ΔR _{1.4 GHz} = 1.75, where the mean ratio is largest, (\bar{R}_1.4\,GHz = -5.81). Total infrared luminosities, L _IR(8-1000 μm), dust temperatures, and dust masses were computed from fitting thermal dust emission modified blackbodies to the mid-infrared (MIR) through submillimeter SEDs. The new results reflect an overall ~0.02 dex lower luminosity than the original IRAS values. Total stellar masses were computed by fitting stellar population synthesis models to the observed near-infrared (NIR) through ultraviolet (UV) SEDs. Mean stellar masses are found to be log (M _sstarf/M _⊙) = 10.79 ± 0.40. Star formation rates have been determined from the infrared (SFR_IR ~ 45 M _⊙ yr^-1) and from the monochromatic UV luminosities (SFR_UV ~ 1.3 M _⊙ yr^-1), respectively. Multi-wavelength active galactic nucleus (AGN) indicators have be used to select putative AGNs: About 60% of the ULIRGs would have been classified as an AGN by at least one of the selection criteria.