AGN feedback in an isolated elliptical galaxy: the effect of strong
  radiative feedback in the kinetic mode
  Based on two-dimensional high resolution hydrodynamic numerical simulation,
we study the mechanical and radiative feedback effects from the central AGN on
the cosmological evolution of an isolated elliptical galaxy. Physical processes
such as star formation and supernovae are considered. The inner boundary of the
simulation domain is carefully chosen so that the fiducial Bondi radius is
resolved and the accretion rate of the black hole is determined
self-consistently. In analogy to previous works, we assume that the specific
angular momentum of the galaxy is low. It is well-known that when the accretion
rates are high and low, the central AGNs will be in cold and hot accretion
modes, which correspond to the radiative and kinetic feedback modes,
respectively. The emitted spectrum from the hot accretion flows is harder than
that from the cold accretion flows, which could result in a higher Compton
temperature accompanied by a more efficient radiative heating, according to
previous theoretical works. Such a difference of the Compton temperature
between the two feedback modes, the focus of this study, has been neglected in
previous works. Significant differences in the kinetic feedback mode are found
as a result of the stronger Compton heating and accretion becomes more chaotic.
More importantly, if we constrain models to correctly predict black hole growth
and AGN duty cycle after cosmological evolution, we find that the favored model
parameters are constrained: mechanical feedback efficiency diminishes with
decreasing luminosity (the maximum efficiency being $\simeq 10^{-3.5}$) and
X-ray Compton temperature increases with decreasing luminosity, although models
with fixed mechanical efficiency and Compton temperature can be found that are
satisfactory as well. We conclude that radiative feedback in the kinetic mode
is much more important than previously thought.
