Witnessing the Formation of a Brightest Cluster Galaxy in a Nearby X-ray Cluster

TL;DR

This study presents detailed multi-wavelength observations of a nearby galaxy cluster, revealing insights into the formation of the brightest cluster galaxy through merging processes and their impact on the cluster environment.

Contribution

It provides new observational evidence of BCG formation via mergers in a nearby cluster, highlighting the role of in situ enrichment and the state of the intracluster medium.

Findings

The cluster retains a cool core with a central metal excess.

Merging galaxies show signs of retained hot gas halos and possible star formation.

The BCG formation involves mergers along large-scale filaments, with modest ICM heating.

Abstract

The central dominant galaxies in galaxy clusters constitute the most massive and luminous galaxies in the Universe. Despite this, the formation of these brightest cluster galaxies (BCGs) and the impact of this on the surrounding cluster environment remain poorly understood. Here we present multi-wavelength observations of the nearby poor X-ray cluster MZ 10451, in which both processes can be studied in unprecedented detail. Chandra observations of the intracluster medium (ICM) in the cluster core, which harbors two optically bright early-type galaxies in the process of merging, show that the system has retained a cool core and a central metal excess. This suggests that any merger-induced ICM heating and mixing remain modest at this stage. Tidally stripped stars seen around either galaxy likely represent an emerging intracluster light component, and the central ICM abundance enhancement may have a prominent contribution from in situ enrichment provided by these stars. The smaller of the merging galaxies shows evidence for having retained a hot gas halo, along with tentative evidence for some obscured star formation, suggesting that not all BCG major mergers at low redshift are completely dissipationless. Both galaxies are slightly offset from the peak of the ICM emission, with all three lying on an axis that roughly coincides with the large-scale elongation of the ICM. Our data are consistent with a picture in which central BCGs are built up by mergers close to the cluster core, by galaxies infalling on radial orbits aligned with the cosmological filaments feeding the cluster.