SIMBAD references

By combining newly obtained infrared photometric data from the All-Sky Data Release of the Wide-field Infrared Survey Explorer with spectroscopic data from the Seventh Data Release of the Sloan Digital Sky Survey, we study the covering factor of warm dust (CFWD) for a large quasar sample, as well as the relations between CFWD and other physical parameters of quasars. We find a strong correlation between the flux ratio in the mid-infrared to near-ultraviolet and the slope of the near-ultraviolet spectra, which is interpreted as a dust extinction effect. After correcting for dust extinction utilizing the above correlation, we examine the relations between CFWD and active galactic nucleus properties: bolometric luminosity (Lbol), black hole mass (MBH) and Eddington ratio (L/LEdd). We confirm the anticorrelation between CFWD and Lbol. Further, we find that CFWD is anticorrelated with MBH but is independent of L/LEdd. Radio-loud quasars are found to follow the same correlations as radio-quiet quasars. Monte Carlo simulations show that the anisotropy of the UV-optical continuum of the accretion disc can have a significant effect, but is not likely to dominate the CFWD-Lbol correlation.