The Interplay of Kinetic and Radiative Feedback in Galaxy Clusters
  Recent observations provide evidence that some cool-core clusters (CCCs) host
quasars in their brightest cluster galaxies (BCGs). Motivated by these findings
we use 3D radiation-hydrodynamic simulations with the code Enzo to explore the
joint role of the kinetic and radiative feedback from supermassive black holes
(SMBHs) in BCGs. We implement kinetic feedback as sub-relativistic plasma
outflows and model radiative feedback using the ray-tracing radiative transfer
or thermal energy injection. In our simulations the central SMBH transitions
between the radiatively efficient and radiatively inefficient states on
timescales of a few Gyr, as a function of its accretion rate. The timescale for
this transition depends primarily on the fraction of power allocated to each
feedback mode, and to a lesser degree on the overall feedback luminosity of the
active galactic nucleus (AGN). Specifically, we find that (a) kinetic feedback
must be present at both low and high accretion rates in order to prevent the
cooling catastrophe, and (b) its contribution likely accounts for > 10% of the
total AGN feedback power, since below this threshold simulated BCGs tend to
host radio-loud quasars most of the time, in apparent contrast with
observations. We also find a positive correlation between the AGN feedback
power and the mass of the cold gas filaments in the cluster core, indicating
that observations of H$\alpha$ filaments can be used as a measure of AGN
feedback.
