Heating Cold Clumps by Jet-inflated Bubbles in Cooling Flow Clusters
  We simulate the evolution of dense-cool clumps embedded in the intra-cluster
medium (ICM) of cooling flow clusters of galaxies in response to multiple
jet-activity cycles, and find that the main heating process of the clumps is
mixing with the hot shocked jets' gas, the bubbles, while shocks have a limited
role. We use the PLUTO hydrodynamical code in two dimensions with imposed
axisymmetry, to follow the thermal evolution of the clumps. We find that the
inflation process of hot bubbles, that appear as X-ray deficient cavities in
observations, is accompanied by complicated induced vortices inside and around
the bubbles. The vorticity induces efficient mixing of the hot bubbles' gas
with the ICM and cool clumps, resulting in a substantial increase of the
temperature and entropy of the clumps. For the parameters used by us heating by
shocks barely competes with radiative cooling, even after 25 consecutive shocks
excited during 0.5 Gyr of simulation. Some clumps are shaped to filamentary
structure that can turn to observed optical filaments. We find that not all
clumps are heated. Those that cool to very low temperatures will fall in and
feed the central supermassive black hole (SMBH), hence closing the feedback
cycle in what is termed the cold feedback mechanism.
