Comparing Simulations of AGN Feedback
  We perform adaptive mesh refinement (AMR) and smoothed particle hydrodynamics
(SPH) cosmological zoom simulations of a region around a forming galaxy
cluster, comparing the ability of the methods to handle successively more
complex baryonic physics. In the simplest, non-radiative case, the two methods
are in good agreement with each other, but the SPH simulations generate central
cores with slightly lower entropies and virial shocks at slightly larger radii,
consistent with what has been seen in previous studies. The inclusion of
radiative cooling, star formation, and stellar feedback leads to much larger
differences between the two methods. Most dramatically, at z=5, rapid cooling
in the AMR case moves the accretion shock well within the virial radius, while
this shock remains near the virial radius in the SPH case, due to excess
heating, coupled with poorer capturing of the shock width. On the other hand,
the addition of feedback from active galactic nuclei (AGN) to the simulations
results in much better agreement between the methods. In this case both
simulations display halo gas entropies of 100 keV cm^2, similar decrements in
the star-formation rate, and a drop in the halo baryon content of roughly 30%.
This is consistent with AGN growth being self-regulated, regardless of the
numerical method. However, the simulations with AGN feedback continue to differ
in aspects that are not self-regulated, such that in SPH a larger volume of gas
is impacted by feedback, and the cluster still has a lower entropy central
core.
