Parsec-scale accretion and winds irradiated by a quasar
  We present numerical simulations of properties of a parsec-scale torus
exposed to illumination by the central black hole in an active galaxy (AGN).
Our physical model allows to investigate the balance between the formation of
winds and accretion simultaneously. Radiation-driven winds are allowed by
taking into account radiation pressure due to UV and IR radiation along with
X-ray heating and dust sublimation. Accretion is allowed through angular
momentum transport and the solution of the equations of radiation
hydrodynamics. Our methods adopt flux-limited diffusion radiation-hydrodynamics
for the dusty, infrared pressure driven part of the flow, along with X-ray
heating and cooling. Angular momentum transport in the accreting part of the
flow is modeled using effective viscosity. Our results demonstrate that
radiation pressure on dust can play an important role in shaping AGN
obscuration. For example, when the luminosity illuminating the torus exceeds
$L>0.01\,L_{\rm Edd}$, where $L_{\rm Edd}$ is the Eddington luminosity, we find
no episodes of sustained disk accretion because radiation pressure does not
allow a disk to form. Despite the absence of the disk accretion, the flow of
gas to smaller radii still proceeds at a rate $10^{-4}-10^{-1}\,M_\odot\,{\rm
yr}^{-1}$ through the capturing of the gas from the hot evaporative flow, thus
providing a mechanism to deliver gas from a radiation-pressure dominated torus
to the inner accretion disk. As $L/L_{\rm edd}$ increases, larger radiation
input leads to larger torus aspect ratios and increased obscuration of the
central black hole. We also find the important role of the X-ray heated gas in
shaping of the obscuring torus.
