MeerKAT-64 discovers wide-spread tidal debris in the nearby NGC 7232 galaxy group

TL;DR

This paper reports the discovery of extensive, previously undetected cold neutral hydrogen tidal debris around the NGC 7232 galaxy group using MeerKAT, revealing complex gas structures and interactions.

Contribution

First high-resolution MeerKAT observations uncover large-scale extsc{HI} streams and debris in the NGC 7232 group, providing new insights into galaxy interactions and gas dynamics.

Findings

extsc{HI} streams extend over 140 kpc, three times the galaxy triplet's size.

The extsc{HI} debris mass is about 6.6 billion solar masses, over half of the triplet's total extsc{HI}.

NGC 7232 and NGC 7233 are extsc{HI} deficient, indicating ongoing interactions.

Abstract

We report the discovery of large amounts of previously undetected cold neutral atomic hydrogen (\HI) around the core triplet galaxies in the nearby NGC~7232 galaxy group with MeerKAT. With a physical resolution of $\sim$1 kpc, we detect a complex web of low surface brightness \HI\ emission down to a 4$\sigma$ column density level of $\sim$1 $\times$ 10$^{19}$ cm$^{-2}$ (over 44 \kms ). The newly discovered H\,{\sc i} streams extend over $\sim$20 arcmin corresponding to 140~kpc in projection. This is $\sim$3 times the \HI\ extent of the galaxy triplet (52 kpc). The \HI\ debris has an \HI\ mass of $\sim$6.6 $\times 10^9$~M$_{\odot}$, more than 50\% of the total \HI\ mass of the triplet. Within the galaxy triplet, NGC~7233 and NGC~7232 have lost a significant amount of \HI\ while NGC~7232B appears to have an excess of \HI. The \HI\ deficiency in NGC~7232 and NGC~7233 indicates that galaxy-galaxy interaction in the group concentrates on this galaxy pair while the other disc galaxies have visited them over time. In comparison to the AMIGA sample of isolated galaxies we find that with regards to its total \HI\ mass the NGC~7232/3 galaxy triplet is not \HI\ deficient. Despite the many interactions associated to the triplet galaxies, no \HI\ seems to have been lost from the group (yet).