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

Article, Preprint English OPEN
McDonald, M. ; McNamara, B. R. ; van Weeren, R. J. ; Applegate, D. E. ; Bayliss, M. ; Bautz, M. W. ; Benson, B. A. ; Carlstrom, J. E. ; Bleem, L. E. ; Chatzikos, M. ; Edge, A. C. ; Fabian, A. C. ; Garmire, G. P. ; Hlavacek-Larrondo, J. ; Jones-Forman, C. ; Mantz, A. B. ; Miller, E. D. ; Stalder, B. ; Veilleux, S. ; Zuhone, J. A. (2015)
  • Publisher: IOP Publishing
  • Related identifiers: doi: 10.1088/0004-637X/811/2/111
  • Subject: Astrophysics - Astrophysics of Galaxies
    arxiv: Astrophysics::Galaxy Astrophysics | Astrophysics::Cosmology and Extragalactic Astrophysics | Astrophysics::High Energy Astrophysical Phenomena

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 (2 × 109 M⊙), young (~4.5 Myr) population of stars, consistent with a time-averaged star formation rate of 610 ± 50 M⊙ yr−1. We report a strong detection of O vi λλ1032,1038, which appears to originate primarily in shock-heated gas, but may contain a substantial contribution (>1000 M⊙ yr−1) from the cooling intracluster medium (ICM). We confirm the presence of deep X-ray cavities in the inner ~10 kpc, which are among the most extreme examples of radio-mode feedback detected to date, implying jet powers of 2–7 × 1045 erg s−1. We provide evidence that the active galactic nucleus 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.