The self-regulated AGN feedback loop: the role of chaotic cold accretion
  Supermassive black hole accretion and feedback play central role in the
evolution of galaxies, groups, and clusters. I review how AGN feedback is
tightly coupled with the formation of multiphase gas and the newly probed
chaotic cold accretion (CCA). In a turbulent and heated atmosphere, cold clouds
and kpc-scale filaments condense out of the plasma via thermal instability and
rain toward the black hole. In the nucleus, the recurrent chaotic collisions
between the cold clouds, filaments, and central torus promote angular momentum
cancellation or mixing, boosting the accretion rate up to 100 times the Bondi
rate. The rapid variability triggers powerful AGN outflows, which quench the
cooling flow and star formation without destroying the cool core. The AGN
heating stifles the formation of multiphase gas and accretion, the feedback
subsides and the hot halo is allowed to cool again, restarting a new cycle.
Ultimately, CCA creates a symbiotic link between the black hole and the whole
host via a tight self-regulated feedback which preserves the gaseous halo in
global thermal equilibrium throughout cosmic time.
