Infrared Spectra and Spectral Energy Distributions for Dusty Starbursts and Active Galactic Nuclei

We present spectroscopic results for all galaxies observed with the Spitzer Infrared Spectrograph (IRS) that also have total infrared fluxes f IR measured with the Infrared Astronomical Satellite (IRAS), also using AKARI photometry when available. Infrared luminosities and spectral energy distributions (SEDs) from 8 μm to 160 μm are compared to polycyclic aromatic hydrocarbon emission from starburst galaxies or mid-infrared dust continuum from active galactic nuclei (AGNs) at rest-frame wavelengths ~8 μm. A total of 301 spectra are analyzed for which IRS and IRAS include the same unresolved source, as measured by the ratio f ν(IRAS 25 μm)/f ν(IRS 25 μm). Sources have 0.004 < z < 0.34 and 42.5 < log L IR < 46.8 (erg s–1) and cover the full range of starburst galaxy and AGN classifications. Individual spectra are provided electronically, but averages and dispersions are presented. We find that log [L IR/νL ν(7.7 μm)] = 0.74 ± 0.18 in starbursts, log [L IR/νL ν(7.7 μm)] = 0.96 ± 0.26 in composite sources (starburst plus AGN), log [L IR/νL ν(7.9 μm)] = 0.80 ± 0.25 in AGNs with silicate absorption, and that log [L IR/νL ν(7.9 μm)] = 0.51 ± 0.21 in AGNs with silicate emission. L IR for the most luminous absorption and emission AGNs are similar and 2.5 times larger than for the most luminous starbursts. AGNs have systematically flatter SEDs than starbursts or composites, but their dispersion in SEDs overlaps starbursts. Sources with the strongest far-infrared luminosity from cool dust components are composite sources, indicating that these sources may contain the most obscured starbursts.