The Covering Factor of Warm Dust in Quasars: View from WISE All-Sky Data Release

TL;DR

This study investigates the warm dust covering factor in quasars using WISE and SDSS data, revealing correlations with luminosity and black hole mass, and accounting for dust extinction effects.

Contribution

It provides a comprehensive analysis of the covering factor of warm dust in quasars, correcting for dust extinction and exploring its relation to key AGN parameters.

Findings

Anti-correlation between covering factor and bolometric luminosity

Covering factor is anti-correlated with black hole mass

No significant dependence of covering factor on Eddington ratio

Abstract

By combining the newly infrared photometric data from the All-Sky Data Release of the Wide-field Infrared Survey Explorer with the spectroscopic data from 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 is independent of $L/L_{\rm Edd}$. Radio-loud quasars are found to follow the same correlations as for radio-quiet quasars. Monte Carlo simulations show that the anisotropy of UV-optical continuum of the accretion disc can significantly affect, but is less likely to dominate the $\CF$--$\Lbol$ correlation.