X-ray properties expected from AGN feedback in elliptical galaxies
  The ISM evolution of elliptical galaxies experiencing feedback from accretion
onto a central black hole was studied recently with high-resolution 1D
hydrodynamical simulations including radiative heating and pressure effects, a
RIAF-like radiative efficiency, mechanical input from AGN winds, and
accretion-driven starbursts. Here we focus on the observational properties of
the models in the X-ray band (nuclear luminosity; hot ISM luminosity and
temperature; temperature and brightness profiles during quiescence and during
outbursts). The nuclear bursts last for ~10^7 yr, with a duty-cycle of a few X
(10^-3-10^-2); the present epoch bolometric nuclear emission is very
sub-Eddington. The ISM thermal luminosity \lx oscillates in phase with the
nuclear one; this helps reproduce statistically the observed large \lx
variation. In quiescence the temperature profile has a negative gradient;
thanks to past outbursts, the brightness profile lacks the steep shape typical
of inflowing models. Outbursts produce disturbances in these profiles. Most
significantly, a hot bubble from shocked hot gas is inflated at the galaxy
center; the bubble would be conical in shape, and show radio emission. The ISM
resumes a smooth appearance on a time-scale of ~200 Myr; the duty-cycle of
perturbances in the ISM is of the order of 5-10%. From the present analysis,
additional input physics is important in the ISM-black hole coevolution, to
fully account for the properties of real galaxies, as a confining external
medium and a jet. The jet will reduce further the mass available for accretion
(and then the Eddington ratio $l$), and may help, together with an external
pressure, to produce flat or positive temperature gradient profiles (observed
in high density environments). Alternatively, $l$ can be reduced if the switch
from high to low radiative efficiency takes place at a larger $l$ than
routinely assumed.
