Gravitational heating, clumps, overheating
  There is no shortage of energy around to solve the overcooling problem of
cooling flow clusters. AGNs, as well as gravitational energy are both energetic
enough to balance the cooling of cores of clusters. The challenge is to couple
this energy to the baryons efficiently enough, and to distribute the energy in
a manner that will not contradict observational constraints of metalicity and
entropy profiles. Here we propose that if a small fraction of the baryons that
are accreted to the cluster halo are in the form of cold clumps, they would
interact with the hot gas component via hydrodynamic drag. We show that such
clumps carry enough energy, penetrate to the center, and heat the core
significantly. We then study the dynamic response of the cluster to this kind
of heating using a 1D hydrodynamic simulation with sub-grid clump heating, and
produce reasonable entropy profile in a dynamic self-consistent way.
