The Mid-Infrared Luminosity Evolution and Luminosity Function of Quasars with SDSS and WISE

Abstract

We determine the 22$\mu$m luminosity evolution and luminosity function for quasars from a data set of over 20,000 objects obtained by combining flux-limited Sloan Digital Sky Survey optical and Wide field Infrared Survey Explorer mid-infrared data. We apply methods developed in previous works to access the intrinsic population distributions non-parametrically, taking into account the truncations and correlations inherent in the data. We find that the population of quasars exhibits positive luminosity evolution with redshift in the mid-infrared, but with considerably less mid-infrared evolution than in the optical or radio bands. With the luminosity evolutions accounted for, we determine the density evolution and local mid-infrared luminosity function. The latter displays a sharp flattening at local luminosities below $\sim 10^{31}$ erg sec$^{-1}$ Hz$^{-1}$, which has been reported previously at 15 $\mu$m for AGN classified as both type-1 and type-2. We calculate the integrated total emission from quasars at 22 $\mu$m and find it to be a small fraction of both the cosmic infrared background light and the integrated emission from all sources at this wavelength.