Subparsec-scale dynamics of a dusty gas disk exposed to anisotropic AGN radiation with frequency-dependent radiative transfer

TL;DR

This study uses advanced radiation hydrodynamic simulations to investigate the complex gas dynamics near the dust sublimation radius of AGN, revealing the formation of a dense, thin disk with high-velocity outflows influenced by anisotropic radiation and X-ray heating.

Contribution

It introduces a comprehensive simulation framework that accounts for frequency-dependent radiative transfer and separate gas and dust temperatures, providing new insights into AGN disk and outflow structures.

Findings

A dense, thin dusty disk forms near the sublimation radius at high Eddington ratios.

IR radiation pressure does not thicken the disk but compresses it, contrary to previous models.

Outflows have mass rates of 0.05-0.1 solar masses per year with low column densities.

Abstract

We explore the gas dynamics near the dust sublimation radius of active galactic nucleus (AGN). For the purpose, we perform axisymmetric radiation hydrodynamic simulations of a dusty gas disk of radius $\approx 1\,\mathrm{pc}$ around a supermassive black hole of mass $10^{7}\,\mathrm{M_{\odot}}$ taking into account (1) anisotropic radiation of accretion disk, (2) X-ray heating by corona, (3) radiative transfer of infrared (IR) photons reemitted by dust, (4) frequency dependency of direct and IR radiations, and (5) separate temperatures for gas and dust. As a result, we find that for Eddington ratio $\approx 0.77$, a nearly neutral, dense ($\approx 10^{6\operatorname{-}8}\;\mathrm{cm^{-3}}$), geometrically-thin ($h/r<0.06$) disk forms with a high velocity ($\approx 200 \sim 3000\;\mathrm{km/s}$) dusty outflow launched from the disk surface. The disk temperature is determined by the balance between X-ray heating and various cooling, and the disk is almost supported by thermal pressure. Contrary to \citet{krolik07:_agn}, the radiation pressure by IR photons is not effective to thicken the disk, but rather compresses it. Thus, it seems difficult for a radiation-supported, geometrically-thick, obscuring torus to form near the dust sublimation radius as far as the Eddington ratio is high ($\sim 1$). The mass outflow rate is $0.05$-$0.1\;\mathrm{M_{\odot}}/\mathrm{yr}$ and the column density of the outflow is $N_{\mathrm{H}}\lesssim 10^{21}\;\mathrm{cm^{-2}}$. To explain observed type-II AGN fraction, it is required that outflow gas is extended to larger radii ($r\gtrsim 10\;\mathrm{pc}$) or that a denser dusty wind is launched from smaller radii ($r\sim 10^{4}\;R_{g}$).