Xiang-Cheng Ma, Ting-Gui Wang
By combining the newly infrared photometric data of the All-Sky Data Release of the Wide Infrared Survey Explorer with the spectroscopic data of the Seventh Data Release of the Sloan Digital Sky Survey, we study the covering factor of warm dust ($\CF$) for a large quasar sample, as well as the relations between $\CF$ and other physical parameters of quasars. We find a strong correlation between the flux ratio of mid-infrared to near-ultraviolet and the slope of near-ultraviolet spectra, which is interpreted as the dust extinction effect. After correcting for the dust extinction utilizing the above correlation, we examine the relations between $\CF$ and AGN properties: bolometric luminosity $\Lbol$, black hole mass $\MBH$ and Eddington ratio $L/L_{\rm Edd}$. We confirm the anti-correlation between $\CF$ and $\Lbol$. Further we find that $\CF$ is anti-correlated with $\MBH$, but independent of $L/L_{\rm Edd}$. Monte Carlo simulations show that the anisotropy of accretion disk can significantly affect, but is unlikely to dominate $\CF$--$\Lbol$ correlation.
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http://arxiv.org/abs/1212.4245
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