Gas Accretion onto a Supermassive Black Hole: a step to model AGN
  feedback
  We study the gas accretion onto a supermassive black hole (SMBH) using the 3D
SPH code GADGET-3 on scales of 0.1-200 pc. First we test our code with
spherically symmetric, adiabatic Bondi accretion problem. We find that our
simulation can reproduce the expected Bondi accretion flow very well for a
limited amount of time until the effect of outer boundary starts to be visible.
We also find artificial heating of gas near the inner accretion boundary due to
the artificial viscosity of SPH. Second, we implement radiative cooling and
heating due to X-rays, and examine the impact of thermal feedback by the
central X-ray source. The accretion flow roughly follows the Bondi solution for
low central X-ray luminosities, however, the flow starts to exhibit
non-spherical fragmentation due to thermal instability for a certain range of
central L_X, and a strong overall outflow develops for greater L_X. The cold
gas develops filamentary structures that fall into the central SMBH, whereas
the hot gas tries to escape through the channels in-between the cold filaments.
Such fragmentation of accreting gas can assist in the formation of clouds
around AGN, induce star-formation, and contribute to the observed variability
of narrow-line regions.
