The relation between line emission and brightest cluster galaxies in three exceptional clusters: evidence for gas cooling from the intracluster medium




There is a strong spatial correlation between brightest clusters galaxies (BCGs) and the peak density and cooling rate of the intracluster 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 ICM, 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 (∼30 K). 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.