IR-derived covering factors for a large sample of quasars from WISE-UKIDSS-SDSS

Abstract

We investigate the range of covering factors (determined from the ratio of IR to UV/optical luminosity) seen in luminous type 1 quasars using a combination of data from the WISE, UKIDSS and SDSS surveys. Accretion disk (UV/optical) and obscuring dust (IR) luminosities are measured via the use of a simple three component SED model. We use these estimates to investigate the distribution of covering factors and its relationship to both accretion luminosity and IR SED shape. The distribution of covering factors (f_C) is observed to be log-normal, with a bias-corrected mean of <log10 f_C>=-0.41 and standard deviation of 0.2. The fraction of IR luminosity emitted in the near-IR (1--5 micron) is found to be high (~40 per cent), and strongly dependant on covering factor.