Modeling AGN Feedback in Cool-Core Clusters: The Balance between Heating
  and Cooling
  We study the long-term evolution of an idealized cool-core galaxy cluster
under the influence of momentum-driven AGN feedback using three-dimensional
high-resolution (60 pc) adaptive mesh refinement (AMR) simulations. The
momentum-driven AGN feedback is modeled with a pair of (small-angle) precessing
jets, and the jet power is calculated based on the accretion rate of the cold
gas in the vicinity of the Supermassive Black Hole (SMBH). The ICM first cools
into clumps along the propagation direction of the AGN jets. As the jet power
increases, gas condensation occurs isotropically, forming spatially extended
(up to a few tens kpc) structures that resemble the observed $\rm H\alpha$
filaments in Perseus and many other cool-core cluster. Jet heating elevates the
gas entropy and cooling time, halting clump formation. The cold gas that is not
accreted onto the SMBH settles into a rotating disk of $\sim 10^{11}$
M$_{\odot}$. The hot gas cools directly onto the cold disk while the SMBH
accretes from the innermost region of the disk, powering the AGN that maintains
a thermally balanced steady state for a few Gyr. The mass cooling rate averaged
over 7 Gyr is $\sim 30$ M$_{\odot}$/yr, an order of magnitude lower than the
classic cooling flow value (which we obtain in runs without the AGN). Medium
resolution simulations produce similar results, but when the resolution is
lower than 0.5 kpc, the cluster experiences cycles of gas condensation and AGN
outbursts. Owing to its self-regulating mechanism, AGN feedback can
successfully balance cooling with a wide range of model parameters. Besides
suppressing cooling, our model produces cold structures in early stages (up to
$\sim 2$ Gyr) that are in good agreement with the observations. However, the
long-lived massive cold disk is unrealistic, suggesting that additional
physical processes are still needed.
