In every proposed unification scheme for Active Galactic Nuclei (AGN), an
integral element is the presence of circumnuclear dust arranged in torus-like
structures. A crucial model parameter in this context is the covering factor
(CF), defined as the ratio between the infrared luminosity of the dusty torus
LIR, and the accretion disk bolometric luminosity
Lagn. Our
study aims to determine whether CF evolution is genuine or if selection effects
significantly influence it. Based on cross-matched multiwavelength
photometrical data from the five major surveys (SDSS, GALEX, UKIDSS, WISE,
SPITZER), a sample of almost 2,000 quasars was derived. The main parameters of
quasars, such as black hole masses and the Eddington ratios, were calculated
based on the spectroscopic data. The data were divided into two redshift bins:
Low-
z (redshift ~1) and High-
z (redshift ~2) quasars.
We identified an issue with the accuracy of the WISE W4 filter. Whenever
feasible, it is recommended to utilize SPITZER MIPS 24
μm data. The
calculated median CF values for the highest quality SPITZER data are comparable
within errors
log CF
low−z=−0.19±0.11 and
log
CF
high−z=−0.18±0.11. The Efron & Petrosian test confirmed the
presence of luminosity evolution with redshift for both
LIR and
Lagn. Both the Low-
z and High-
z samples exhibit a similar
correlation between
Lagn and
LIR. No discernible evolution of
the CF was observed in the subsample of quasars with high SMBH mass bin or high
luminosities. The relationship between
LIR and
Lagn deviates
slightly from the expected 1:1 scaling. However, no statistically significant
dependence of CF on luminosities could be claimed across the entire dataset.