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

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 Wide-Field Infrared Survey Explorer, UKIDSS and SDSS surveys. Accretion disc (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 < log(10) f(C) > = - 0.41 and standard deviation of sigma = 0.2. The fraction of IR luminosity emitted in the near-IR (1-5 mu m) is found to be high (similar to 40 per cent), and strongly dependant on covering factor.