Simulating the Cooling Flow of Cool-Core Clusters
  We carry out high-resolution adaptive mesh refinement simulations of a cool
core cluster, resolving the flow from Mpc scales down to pc scales. We do not
(yet) include any AGN heating, focusing instead on cooling in order to
understand how gas gets to the supermassive black hole (SMBH) at the center of
the cluster. We find that, as the gas cools, the cluster develops a very flat
temperature profile, undergoing a cooling catastrophe only in the central
10-100 pc of the cluster. Outside of this region, the flow is smooth, with no
local cooling instabilities, and naturally produces very little low-temperature
gas (below a few keV), in agreement with observations. The gas cooling in the
center of the cluster rapidly forms a thin accretion disk. The amount of cold
gas produced at the very center grows rapidly until a reasonable estimate of
the resulting AGN heating rate (assuming even a moderate accretion efficiency)
would overwhelm cooling. We argue that this naturally produces a thermostat
which links the cooling of gas out to 100 kpc with the cold gas accretion in
the central 100 pc, potentially closing the loop between cooling and heating.
Isotropic heat conduction does not affect the result significantly, but we show
that including the potential well of the brightest cluster galaxy is necessary
to obtain the correct result. Also, we found that the outcome is sensitive to
resolution, requiring very high mass resolution to correctly reproduce the
small transition radius.
