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