Directly Imaging the Cooling Flow in the Phoenix Cluster

TL;DR

This study uses JWST observations to map intermediate-temperature gas in the Phoenix galaxy cluster, revealing recent rapid cooling episodes and emphasizing the complex role of black hole feedback in cluster gas dynamics.

Contribution

First large-scale mapping of 10^5-10^6 K gas in a galaxy cluster core, linking cooling episodes with star formation and feedback processes.

Findings

Detected extended [Ne VI] emission aligned with cooling regions

Estimated a recent cooling rate spike of 5,000-23,000 solar masses per year

Highlighted the role of black hole feedback in both regulating and promoting cooling

Abstract

In the centers of many galaxy clusters, the hot ($\sim$10$^7$ K) intracluster medium (ICM) can become dense enough that it should cool on short timescales. However, the low measured star formation rates in massive central galaxies and absence of soft X-ray lines from cooling gas suggest that most of this gas never cools - this is known as the "cooling flow problem." The latest observations suggest that black hole jets are maintaining the vast majority of gas at high temperatures. A cooling flow has yet to be fully mapped through all gas phases in any galaxy cluster. Here, we present new observations of the Phoenix cluster using the James Webb Space Telescope to map the [Ne VI] $\lambda$7.652$\mu$m emission line, allowing us to probe gas at 10$^{5.5}$ K on large scales. These data show extended [Ne VI] emission cospatial with (i) the cooling peak in the ICM, (ii) the coolest gas phases, and (iii) sites of active star formation. Taken together, these imply a recent episode of rapid cooling, causing a short-lived spike in the cooling rate which we estimate to be 5,000-23,000 M$_\odot$ yr$^{-1}$. These data provide the first large-scale map of gas at temperatures between 10$^5$-10$^6$ K in a cluster core, and highlight the critical role that black hole feedback plays in not only regulating but also promoting cooling.