Updated picture of the active galactic nuclei with dusty/dust-free gas structures and effects of the radiation pressure

Abstract

This study investigates the properties of two gas structures of X-ray selected active galactic nuclei (AGNs), that is, dusty and dust-free gas components, by separating them with the line-of-sight dust extinction (AV ) and the neutral gas column density (NH). The typical column density of the dusty and dust-free gas differs depending on the Seyfert type, indicating that both structures have anisotropic column density distributions. The number of targets with the dusty gas column density (NH,d) of log NH,d [cm−2] > 23 is much smaller than that with the same column density of the dust-free gas. This result indicates that the optically thick part of the dusty gas structure is very thin. There are very few targets with a larger Eddington ratio (fEdd) than the effective Eddington limit of the dusty gas and the covering factor of the dusty gas with 22 ≤ log NH,d [cm−2] < 24 exhibits a clear drop at the effective Eddington limit. These results support the scenario wherein the covering factor of the dusty torus decreases in a high Eddington ratio owing to the radiation-driven dusty gas outflow. The covering factor of the dust-free gas with the column density (NH,df) of 22 ≤ log NH,df [cm−2] < 24 similarly exhibits the decrease in high Eddington ratio, although it may be owing to the dust-free gas outflow driven by certain other mechanisms than the radiation pressure. Finally, we propose an updated picture of the AGN gas structure based on our results and the literature.