HI absorption associated with Norma's brightest cluster galaxy

TL;DR

This study reports the detection of atomic hydrogen absorption in the brightest cluster galaxy of the Norma cluster, providing insights into cold gas properties and galaxy-cluster interactions.

Contribution

First detection of HI absorption in ESO 137-G006, revealing cold gas characteristics and suggesting recent infall of the galaxy into the cluster core.

Findings

HI absorption line detected in ESO 137-G006

Gas column density estimated at ~1.3 x 10^{20} T_spin atoms cm^{-2}

Supports the scenario of recent galaxy infall into the cluster

Abstract

ESO 137-G006 is the brightest cluster galaxy (BCG) of the cool-core and dynamically young Norma cluster. We discover an atomic hydrogen (HI) 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, $T_{\rm{spin}} \leq 194$ K, consistent with the HI 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.