SPECTRAL ENERGY DISTRIBUTIONS OF LOCAL LUMINOUS AND ULTRALUMINOUS INFRARED GALAXIES

Abstract

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 ν L ν (60 μm)/ν L 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[ν L ν (λ)/ν L ν (60 μm)], observed over the full sample is seen in the hard X-rays (HX = 2–10 keV), where Δ R HX = 3.73 ( ). A small range is found in the radio (1.4 GHz), Δ R 1.4 GHz = 1.75, where the mean ratio is largest, ( ). 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 ⋆ / 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.