Deep Chandra, HST-COS, and Megacam Observations of the Phoenix Cluster:
  Extreme Star Formation and AGN Feedback on Hundred Kiloparsec Scales
  We present new ultraviolet, optical, and X-ray data on the Phoenix galaxy
cluster (SPT-CLJ2344-4243). Deep optical imaging reveals previously-undetected
filaments of star formation, extending to radii of ~50-100 kpc in multiple
directions. Combined UV-optical spectroscopy of the central galaxy reveals a
massive (2x10^9 Msun)), young (~4.5 Myr) population of stars, consistent with a
time-averaged star formation rate of 610 +/- 50 Msun/yr. We report a strong
detection of OVI(1032,1038) which appears to originate primarily in
shock-heated gas, but may contain a substantial contribution (>1000 Msun/yr)
from the cooling intracluster medium. We confirm the presence of deep X-ray
cavities in the inner ~10 kpc, which are amongst the most extreme examples of
radio-mode feedback detected to date, implying jet powers of 2-7 x10^45 erg/s.
We provide evidence that the AGN inflating these cavities may have only
recently transitioned from "quasar-mode" to "radio-mode", and may currently be
insufficient to completely offset cooling. A model-subtracted residual X-ray
image reveals evidence for prior episodes of strong radio-mode feedback at
radii of ~100 kpc, with extended "ghost" cavities indicating a prior epoch of
feedback roughly 100 Myr ago. This residual image also exhibits significant
asymmetry in the inner ~200 kpc (0.15R500), reminiscent of infalling cool
clouds, either due to minor mergers or fragmentation of the cooling ICM. Taken
together, these data reveal a rapidly evolving cool core which is rich with
structure (both spatially and in temperature), is subject to a variety of
highly energetic processes, and yet is cooling rapidly and forming stars along
thin, narrow filaments.
