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

TL;DR

This study analyzes the covering factors of luminous quasars using IR, UV, and optical data from WISE, UKIDSS, and SDSS, revealing a log-normal distribution and a strong dependence of IR emission on covering factor.

Contribution

It provides the first large-sample analysis of IR-derived covering factors in quasars, linking IR SED shape and luminosity to obscuring dust geometry.

Findings

Covering factors follow a log-normal distribution with mean -0.41.

Near-IR emission (~40%) depends strongly on covering factor.

Distribution of covering factors correlates with IR SED shape.

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.