Mechanical AGN Feedback: Controlling the Thermodynamical Evolution of
  Elliptical Galaxies
  A fundamental gap in the current understanding of galaxies concerns the
thermodynamical evolution of the ordinary, baryonic matter. On one hand,
radiative emission drastically decreases the thermal energy content of the
interstellar plasma (ISM), inducing a slow cooling flow toward the centre. On
the other hand, the active galactic nucleus (AGN) struggles to prevent the
runaway cooling catastrophe, injecting huge amount of energy in the ISM. The
present study intends to deeply investigate the role of mechanical AGN feedback
in (isolated or massive) elliptical galaxies, extending and completing the mass
range of tested cosmic environments. Our previously successful feedback models,
in galaxy clusters and groups, demonstrated that AGN outflows, self-regulated
by cold gas accretion, are able to properly quench the cooling flow, without
destroying the cool core. Via 3D hydrodynamic simulations (FLASH 3.3),
including also stellar evolution, we show that massive mechanical AGN outflows
can indeed solve the cooling flow problem for the entire life of the galaxy, at
the same time reproducing typical observational features and constraints, such
as buoyant underdense bubbles, elliptical shock cocoons, sonic ripples,
dredge-up of metals, subsonic turbulence, and extended filamentary or nuclear
cold gas. In order to avoid overheating and totally emptying the isolated
galaxy, the frequent mechanical AGN feedback should be less powerful and
efficient (~1.e-4), compared to the heating required for more massive and bound
ellipticals surrounded by the intragroup medium (efficiency ~1.e-3).
