AGN obscuration through dusty infrared dominated flows. I. Radiation-hydrodynamics solution for the wind

TL;DR

This paper develops a radiation-hydrodynamics model showing that infrared radiation pressure can support a dense, dusty wind at parsec scales in active galactic nuclei, explaining obscuration and feedback mechanisms.

Contribution

It introduces a numerical 2D radiation transfer model coupled with wind calculations, demonstrating infrared radiation pressure can produce thick obscuring winds in AGNs.

Findings

Infrared radiation pressure supports thick obscuration in AGNs.

Outflows driven by IR radiation can reach or exceed escape velocity.

Failed winds are significant in Compton thick models.

Abstract

We construct a radiation-hydrodynamics model for the obscuring toroidal structure in active galactic nuclei. In this model the obscuration is produced at parsec scale by a dense, dusty wind which is supported by infrared radiation pressure on dust grains. To find the distribution of radiation pressure, we numerically solve the 2D radiation transfer problem in a flux limited diffusion approximation. We iteratively couple the solution with calculations of stationary 1D models for the wind, and obtain the z-component of the velocity. Our results demonstrate that for AGN luminosities greater than 0.1 Ledd external illumination can support a geometrically thick obscuration via outflows driven by infrared radiation pressure. The terminal velocity of marginally Compton-thin models (0.2<tau_T<0.6), is comparable to or greater than the escape velocity. In Compton thick models the maximum value of the vertical component of the velocity is lower than the escape velocity, suggesting that a significant part of our torus is in the form of failed wind. The results demonstrate that obscuration via normal or failed infrared-driven winds is a viable option for the AGN torus problem and AGN unification models. Such winds can also provide an important channel for AGN feedback.