Anatomy of a Cooling Flow: The Feedback Response to Pure Cooling in the Core of the Phoenix Cluster

Abstract

We present new, deep observations of the Phoenix cluster from Chandra , 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 over previous observations at X-ray, optical, and radio wavelengths. We find that the one-dimensional temperature and entropy profiles are consistent with expectations for pure-cooling models. In particular, the entropy profile is well fit by a single power law at all radii, with no evidence for excess entropy in the core. In the inner ∼10 kpc, the cooling time is shorter than any other known cluster by an order of magnitude, while the ratio of the cooling time to freefall time ( t cool / t ff ) approaches unity, signaling that the intracluster medium is unable to resist multiphase condensation on kpc scales. The bulk of the cooling in the inner ∼20 kpc is confined to a low-entropy filament extending northward from the central galaxy, with t cool / t ff  ∼ 1 over the length of the filament. In this filament, we find evidence for ∼10 10 M ⊙ in cool (∼10 4 K) gas (as traced by the [O ii ] λλ 3726,3729 doublet), which is coincident with the low-entropy filament and absorbing soft X-rays. 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. These data support a picture in which active galactic nucleus feedback is promoting the formation of a multiphase medium via uplift of low-entropy gas, either via ordered or chaotic (turbulent) motions.