Radiation-driven outflows from and radiative support in dusty tori of active galactic nuclei

TL;DR

This study uses 3D radiative hydrodynamics simulations to investigate how radiation pressure on dust influences the structure and outflows of dusty tori in active galactic nuclei, revealing dynamic, clumpy, and wind-driving behaviors.

Contribution

It introduces detailed 3D simulations of AGN tori including IR and UV radiation transfer, demonstrating radiation-driven winds and structural features not previously modeled in such detail.

Findings

UV radiation pressure launches strong winds along the inner surface.

IR radiation escapes mainly through the central hole, creating anisotropy.

The torus exhibits non-axisymmetric features and clumping due to radiation effects.

Abstract

Substantial evidence points to dusty, geometrically thick tori obscuring the central engines of active galactic nuclei (AGNs), but so far no mechanism satisfactorily explains why cool dust in the torus remains in a puffy geometry. Near-Eddington infrared (IR) and ultraviolet (UV) luminosities coupled with high dust opacities at these frequencies suggest that radiation pressure on dust can play a significant role in shaping the torus. To explore the possible effects of radiation pressure, we perform three-dimensional radiative hydrodynamics simulations of an initially smooth torus. Our code solves the hydrodynamics equations, the time-dependent multi-angle group IR radiative transfer (RT) equation, and the time-independent UV RT equation. We find a highly dynamic situation. IR radiation is anisotropic, leaving primarily through the central hole. The torus inner surface exhibits a break in axisymmetry under the influence of radiation and differential rotation; clumping follows. In addition, UV radiation pressure on dust launches a strong wind along the inner surface; when scaled to realistic AGN parameters, this outflow travels at $\sim 5000 (M/10^7 M_\odot)^{1/4} [L_\mathrm{UV}/(0.1 L_\mathrm E)]^{1/4} \mathrm{km}\,\mathrm s^{-1}$ and carries $\sim 0.1 (M/10^7 M_\odot)^{3/4} [L_\mathrm{UV}/(0.1 L_\mathrm E)]^{3/4} M_\odot\,\mathrm{yr}^{-1}$, where $M$, $L_\mathrm{UV}$, and $L_\mathrm E$ are the mass, UV luminosity, and Eddington luminosity of the central object respectively.