Warm and cold molecular gas in the cluster center of MACS 1931-26 with JWST and ALMA

Abstract

We perform one of the first spatially resolved studies of warm ($>$100 K) and cold (10-100 K) molecular gas in the circumgalactic medium (CGM), focusing on the brightest cluster galaxy (BCG) of a cool-core galaxy cluster, MACS1931-26 at z=0.35. This galaxy has a massive H$_2$ reservoir and a radio-loud active galactic nucleus (AGN) and is undergoing a starburst event. We present new JWST observations of this system, revealing warm H$_2$ gas that is co-spatial with the cold molecular gas traced by CO, extending over 30 kpc around the BCG in a tail-like structure reaching into the circumgalactic medium of this galaxy. Analysis of the mid-infrared pure H$_2$ rotational lines H$_2$S(1), H$_2$S(5), and H$_2$S(9) indicate warm gas temperatures of $515.6 \pm 0.8$ K and $535.2\pm 1.9$ K in the BCG and tail regions, respectively. We compare cold gas, traced by the CO(3-2) observed with ALMA, to the warm gas traced by JWST. The warm-to-cold molecular gas fraction is comparable in the BCG ($1.4\%\pm0.2\%$) and the CGM tail ($1.9\%\pm0.3\%$). Our analysis suggests that the dissipation of the kinetic energy of the H$_2$-emitting gas is sufficient to lead to the formation of the CO gas. This observation provides new insights into the molecular gas distribution and its potential role in the interplay between the central galaxy and its circumgalactic environment.