BASS XLII: The relation between the covering factor of dusty gas and the Eddington ratio in nearby active galactic nuclei

TL;DR

This study analyzes the relationship between the covering factor of dusty gas around supermassive black holes and their Eddington ratio in nearby active galactic nuclei, confirming that higher accretion rates lead to less obscuring material.

Contribution

It provides observational evidence linking the covering factor of dusty gas to the Eddington ratio using infrared and X-ray data for a large AGN sample, supporting radiation-regulated SMBH growth models.

Findings

Covering factor decreases with increasing Eddington ratio.

Obscured AGN have larger covering factors than unobscured ones.

Median covering factors align with radiation-regulated growth predictions.

Abstract

Accreting supermassive black holes (SMBHs) located at the center of galaxies are typically surrounded by large quantities of gas and dust. The structure and evolution of this circumnuclear material can be studied at different wavelengths, from the submillimeter to the X-rays. Recent X-ray studies have shown that the covering factor of the obscuring material tends to decrease with increasing Eddington ratio, likely due to radiative feedback on dusty gas. Here we study a sample of 549 nearby (z<0.1) hard X-ray (14-195 keV) selected non-blazar active galactic nuclei (AGN), and use the ratio between the AGN infrared and bolometric luminosity as a proxy of the covering factor. We find that, in agreement with what has been found by X-ray studies of the same sample, the covering factor decreases with increasing Eddington ratio. We also confirm previous findings which showed that obscured AGN typically have larger covering factors than unobscured sources. Finally, we find that the median covering factors of AGN located in different regions of the column density-Eddington ratio diagram are in good agreement with what would be expected from a radiation-regulated growth of SMBHs.