AGN feedback in elliptical galaxies: numerical simulations
  The importance of feedback (radiative and mechanical) from massive black
holes at the centers of elliptical galaxies is not in doubt, given the well
established relation among black hole mass and galaxy optical luminosity. Here,
with the aid of high-resolution hydrodynamical simulations, we discuss how this
feedback affects the hot ISM of isolated elliptical galaxies of different mass.
The cooling and heating functions include photoionization plus Compton heating,
the radiative transport equations are solved, and the mechanical feedback due
to the nuclear wind is also described on a physical basis; star formation is
considered. In the medium-high mass galaxies the resulting evolution is highly
unsteady. At early times major accretion episodes caused by cooling flows in
the recycled gas produced by stellar evolution trigger AGN flaring: relaxation
instabilities occur so that duty cycles are small enough to account for the
very small fraction of massive ellipticals observed to be in the QSO-phase,
when the accretion luminosity approaches the Eddington luminosity. At low
redshift all models are characterized by smooth, very sub-Eddington mass
accretion rates. The mass accumulated by the central black hole is limited to
range observed today, even though the mass lost by the evolving stellar
population is roughly two order of magnitude larger than the black hole masses
observed in elliptical galaxies.
