An Investigation into the Effects of Luminosity on the Mid‐Infrared Spectral Energy Distributions of Radio‐quiet Quasars

We present an analysis of the effects of luminosity on the shape of themid-infrared spectral energy distributions (SEDs) of 234 radio-quiet quasarsoriginally presented by Richards et al. In quasars without evident dustextinction, the spectrally integrated optical and infrared luminosities arelinearly correlated over nearly three decades in luminosity. We find asignificant (>99.99% confidence) correlation between the 1.8-8.0 micronspectral index and infrared luminosity that indicates an enhancement of themid-infrared continuum with increasing luminosity. Coupled with strong evidencefor spectral curvature in more luminous quasars, we conclude this trend islikely a manifestation of the `near-infrared (3-5 micron) bump' noticed inearlier quasar SED surveys. The strength of this feature is indicative of thecontribution of emission from the hottest (>1000 K) dust to the mid-infraredspectrum; higher luminosity quasars tend to show more hot dust emission.Finally, the comparable distribution of bolometric corrections from themonochromatic 3 micron luminosity as well as its lack of sensitivity to dustextinction as compared to the standard bolometric correction from nu*L_{5100A}suggest that the former may be a more robust indicator of bolometric quasarluminosity. The close link between the power in the mid-infrared and opticaland the effect of luminosity on the shape of the mid-infrared continuumindicate that considering mid-infrared emission independent of the propertiesof the quasar itself is inadequate for understanding the parsec-scale quasarenvironment.Comment: Comments: 13 pages, 11 figures (3 color), uses emulateapj. Accepted for publication in Ap