The Relation Between Line Emission and Brightest Cluster Galaxies in Three Exceptional Clusters: Evidence for Gas Cooling from the ICM

TL;DR

This study investigates the relationship between gas cooling in galaxy clusters and the presence of cold gas and emission in brightest cluster galaxies, especially in cases with spatial offsets, revealing a causal link between ICM cooling and molecular gas formation.

Contribution

It provides new evidence of gas cooling and molecular gas formation in clusters with offset BCGs, highlighting the impact of transient events on cluster dynamics.

Findings

Optical line emission coincides with soft X-ray peaks.

Cooling persists in offset regions, indicating ongoing ICM cooling.

A causal link exists between low-temperature ICM gas and molecular gas.

Abstract

There is a strong spatial correlation between brightest cluster galaxies (BCGs) and the peak density and cooling rate of the intra-cluster medium (ICM). In this paper we combine integral field spectroscopy, CO observations and X-ray data to study three exceptional clusters (Abell 1991, Abell 3444 and Ophiuchus) where there is a physical and dynamical offset between the BCG and the cooling peak to investigate the connection between the cooling of the intracluster medium, the cold gas being deposited and the central galaxy. We find the majority of the optical line emission is spatially coincident with the peak in the soft X-rays. In the case of A1991 we make separate detections of CO(2-1) emission on the BCG and on the peak of the soft X-ray emission suggesting that cooling continues to occur in the core despite being offset from the BCG. We conclude that there is a causal link between the lowest temperature (< 2 keV) ICM gas and the molecular gas(~ 30K). This link is only apparent in systems where a transitory event has decoupled the BCG from the soft X-ray peak. We discuss the prospects for identifying more examples of this rare configuration.