Deep Chandra, HST-COS, and Megacam Observations of the Phoenix Cluster: Extreme Star Formation and AGN Feedback on Hundred Kiloparsec Scales

TL;DR

This study presents multi-wavelength observations of the Phoenix galaxy cluster, revealing extreme star formation, complex feedback processes, and dynamic cool core structures influenced by AGN activity and cooling flows.

Contribution

It provides new detailed imaging and spectroscopic data showing the interplay of star formation, AGN feedback, and cooling in the Phoenix cluster, highlighting recent feedback episodes and filamentary structures.

Findings

Discovery of star-forming filaments extending 50-100 kpc.

Detection of deep X-ray cavities indicating powerful AGN jets.

Evidence of prior feedback episodes and complex cool core dynamics.

Abstract

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.