Anatomy of a Cooling Flow: The Feedback Response to Pure Cooling in the
  Core of the Phoenix Cluster
  We present new, deep observations of the Phoenix cluster from the Chandra
X-ray Observatory, the Hubble Space Telescope, and the Karl Jansky Very Large
Array. These data provide an order of magnitude improvement in depth and/or
angular resolution at X-ray, optical, and radio wavelengths, yielding an
unprecedented view of the core of the Phoenix cluster. We find that the
one-dimensional temperature and entropy profiles are consistent with
expectations for pure-cooling hydrodynamic simulations and analytic
descriptions of homogeneous, steady-state cooling flow models. In the inner ~10
kpc, the cooling time is shorter by an order of magnitude than any other known
cluster, while the ratio of the cooling time to freefall time approaches unity,
signaling that the ICM is unable to resist multiphase condensation on kpc
scales. When we consider the thermodynamic profiles in two dimensions, we find
that the cooling is highly asymmetric. The bulk of the cooling in the inner ~20
kpc is confined to a low-entropy filament extending northward from the central
galaxy. We detect a substantial reservoir of cool (10^4 K) gas (as traced by
the [OII] doublet), which is coincident with the low-entropy filament. The bulk
of this cool gas is draped around and behind a pair of X-ray cavities,
presumably bubbles that have been inflated by radio jets, which are detected
for the first time on kpc scales. These data support a picture in which AGN
feedback is promoting the formation of a multiphase medium via a combination of
ordered buoyant uplift and locally enhanced turbulence. These processes ought
to counteract the tendency for buoyancy to suppress condensation, leading to
rapid cooling along the jet axis. The recent mechanical outburst has sufficient
energy to offset cooling, and appears to be coupling to the ICM via a cocoon
shock, raising the entropy in the direction orthogonal to the radio jets.
