# The Dust and Molecular Gas in the Brightest Cluster Galaxy in MACS 1931.8-2635

## TL;DR

This study uses ALMA observations to analyze the molecular gas and dust in the brightest cluster galaxy of MACS 1931.8-2635, revealing a large cold gas reservoir, complex gas dynamics, and insights into star formation and AGN feedback.

## Contribution

First detailed ALMA study of molecular gas and dust in this BCG, revealing extensive cold gas, complex kinematics, and dust properties influenced by star formation and AGN activity.

## Key findings

- Detected $1.9 imes 10^{10}$ M$_{igodot}$ of molecular gas
- Molecular gas extends up to 30 kpc, tracing UV knots and filaments
- Dust temperature constrained to be below 10 K, indicating cold dust outside the ICM interaction zone

## Abstract

We present new ALMA observations of the molecular gas and far-infrared continuum around the brightest cluster galaxy (BCG) in the cool-core cluster MACS 1931.8-2635. Our observations reveal $1.9 \pm 0.3 \times 10^{10}$ M$_{\odot}$ of molecular gas, on par with the largest known reservoirs of cold gas in a cluster core. We detect CO(1-0), CO(3-2), and CO(4-3) emission from both diffuse and compact molecular gas components that extend from the BCG center out to $\sim30$ kpc to the northwest, tracing the UV knots and H$\alpha$ filaments observed by HST. Due to the lack of morphological symmetry, we hypothesize that the $\sim300$ km s$^{-1}$ velocity of the CO in the tail is not due to concurrent uplift by AGN jets, rather we may be observing the aftermath of a recent AGN outburst. The CO spectral line energy distribution suggests that molecular gas excitation is influenced by processes related to both star formation and recent AGN feedback. Continuum emission in Bands 6 and 7 arises from dust and is spatially coincident with young stars and nebular emission observed in the UV and optical. We constrain the temperature of several dust clumps to be $\lesssim 10$ K, which is too cold to be directly interacting with the surrounding $\sim 4.8$ keV intracluster medium (ICM). The cold dust population extends beyond the observed CO emission and must either be protected from interacting with the ICM or be surrounded by local volumes of ICM that are several keV colder than observed by Chandra.