H i absorption associated with Norma’s brightest cluster galaxy

Abstract

ABSTRACT ESO 137-G006 is the brightest cluster galaxy (BCG) of the cool-core and dynamically young Norma cluster. We discover an atomic hydrogen (H i) absorption line associated with this BCG using the Australia Telescope Compact Array. We estimate a gas column density of $\approx (1.3 \pm 0.2) \times 10^{20}\, T_{\rm {spin}}$ atoms cm−2 with spin temperature, Tspin ≤ 194 K, consistent with the H i properties of other early-type galaxies and cool-core cluster BCGs. The relationship between the presence of cold gas and a cluster cooling flow is unclear. Our results support the scenario that ESO 137-G006 may be a recent arrival to the cluster centre and not the original BCG. This scenario is consistent with the observed spatial alignment of the BCG’s wide-angle tail radio lobes with Norma’s X-ray sub-cluster and the significant line-of-sight velocity offset between the mean velocity of Norma and that of the BCG.