AGN jet-driven stochastic cold accretion in cluster cores
  Several arguments suggest that stochastic condensation of cold gas and its
accretion onto the central supermassive black hole (SMBH) is essential for
active galactic nuclei (AGN) feedback to work in the most massive galaxies that
lie at the centres of galaxy clusters. Our 3-D hydrodynamic AGN jet-ICM
(intracluster medium) simulations, looking at the detailed angular momentum
distribution of cold gas and its time variability for the first time, show that
the angular momentum of the cold gas crossing $\lesssim 1$ kpc is essentially
isotropic. With almost equal mass in clockwise and counter-clockwise
orientations, we expect a cancellation of angular momentum on roughly the
dynamical time. This means that a compact accretion flow with a short viscous
time ought to form, through which enough accretion power can be channeled into
jet mechanical energy sufficiently quickly to prevent a cooling flow. The
inherent stochasticity, expected in feedback cycles driven by cold gas
condensation, gives rise to a large variation in the cold gas mass at the
centres of galaxy clusters, for similar cluster and SMBH masses, in agreement
with the observations. Such correlations are expected to be much tighter for
the smoother hot/Bondi accretion. The weak correlation between cavity power and
Bondi power obtained from our simulations also match observations.
