AGN feedback and the origin and fate of the hot gas in early-type
  galaxies
  A recent determination of the relationships between the X-ray luminosity of
the ISM (Lx) and the stellar and total mass, for a sample of nearby early-type
galaxies (ETGs), is used to investigate the origin of the hot gas, via a
comparison with the results of hydrodynamical simulations of the ISM evolution
for a large set of isolated ETGs. After the epoch of major galaxy formation
(after z~2), the ISM is replenished by stellar mass losses and SN ejecta, at
the rate predicted by stellar evolution, and is depleted by star formation; it
is heated by the thermalization of stellar motions, SNe explosions and the
mechanical (from winds) and radiative AGN feedback. The models agree well with
the observed relations, even for the largely different Lx values at the same
mass, thanks to the sensitivity of the gas flow to many galaxy properties; this
holds for models including AGN feedback, and those without. Therefore, the mass
input from the stellar population is able to account for a major part of the
observed Lx; and AGN feedback, while very important to maintain massive ETGs in
a time-averaged quasi-steady state, keeping low star formation and the black
hole mass, does not dramatically alter the gas content originating in stellar
recycled material. These conclusions are based on theoretical predictions for
the stellar population contributions in mass and energy, and on a
self-consistent modeling of AGN feedback.
