Redefining the torus: A unifying view of AGN in the infrared and sub-mm

TL;DR

This paper proposes a unifying model for AGN tori, combining IR and sub-mm observations, where a dusty disk and wind driven by radiation pressure explain the observed structures and obscuration.

Contribution

It introduces a comprehensive physical model unifying IR and sub-mm observations of AGN tori, emphasizing the role of radiation pressure-driven winds.

Findings

Dusty molecular gas flows inward via a disk with small to moderate scale height.

Radiation pressure causes the inner disk to puff up and launch a dusty wind.

The dusty wind feeds back mass into the galaxy at rates depending on AGN luminosity.

Abstract

The advent of high-angular resolution IR and sub-mm interferometry allows for spatially-resolved observations of the parsec-scale environment of active galactic nuclei (AGN), commonly referred to as the "torus." While molecular lines show the presence of large, massive disks, the IR observations appear to be dominated by a strong polar component that has been interpreted as a dusty wind. This paper aims at using characteristics shared by AGN in each of the wavebands and a set of simple physical principles to form a unifying view of these seemingly contradictory observations: Dusty molecular gas flows in from galactic scales of ~100 pc to the sub-parsec environment via a disk with small to moderate scale height. The hot, inner part of the disk puffs up due to IR radiation pressure and unbinds a large amount of the inflowing gas from the black hole's gravitational potential, providing the conditions to launch a wind driven by the radiation pressure from the AGN. The dusty wind feeds back mass into the galaxy at a rate of the order of ~0.1-100 $M_\odot$/yr, depending on AGN luminosity and Eddington ratio. Angle-dependent obscuration as required by AGN unification is provided by a combination of disk, wind, and wind launching region.