ALMA observations of massive molecular gas filaments encasing radio bubbles in the Phoenix cluster

TL;DR

ALMA observations reveal that radio bubbles in the Phoenix cluster are encased by massive, ordered molecular gas filaments, indicating a close coupling between feedback processes and cold gas dynamics that regulate galaxy evolution.

Contribution

This study provides the first detailed ALMA imaging of molecular filaments around radio bubbles, demonstrating their role in galaxy feedback mechanisms.

Findings

Molecular filaments are aligned with radio bubble peripheries.

Gas flows along filaments are ordered and not gravitationally free-falling.

Radio bubbles lift or induce formation of cold molecular gas.

Abstract

We report new ALMA observations of the CO(3-2) line emission from the $2.1\pm0.3\times10^{10}\rm\thinspace M_{\odot}$ molecular gas reservoir in the central galaxy of the Phoenix cluster. The cold molecular gas is fuelling a vigorous starburst at a rate of $500-800\rm\thinspace M_{\odot}\rm\; yr^{-1}$ and powerful black hole activity in the form of both intense quasar radiation and radio jets. The radio jets have inflated huge bubbles filled with relativistic plasma into the hot, X-ray atmospheres surrounding the host galaxy. The ALMA observations show that extended filaments of molecular gas, each $10-20\rm\; kpc$ long with a mass of several billion solar masses, are located along the peripheries of the radio bubbles. The smooth velocity gradients and narrow line widths along each filament reveal massive, ordered molecular gas flows around each bubble, which are inconsistent with gravitational free-fall. The molecular clouds have been lifted directly by the radio bubbles, or formed via thermal instabilities induced in low entropy gas lifted in the updraft of the bubbles. These new data provide compelling evidence for close coupling between the radio bubbles and the cold gas, which is essential to explain the self-regulation of feedback. The very feedback mechanism that heats hot atmospheres and suppresses star formation may also paradoxically stimulate production of the cold gas required to sustain feedback in massive galaxies.