Environmental processing of galaxies in HI-rich groups

TL;DR

This study investigates the atomic hydrogen content of 13 HI-rich galaxy groups, revealing environmental effects like tidal stripping and mergers that influence galaxy evolution regardless of their larger cosmic environment.

Contribution

It provides new insights into how tidal interactions and mergers affect HI content in galaxy groups, highlighting environmental processing mechanisms in diverse settings.

Findings

HI mass fraction varies widely among galaxies in the groups.

Environmental processing affects HI content more than mid-infrared properties.

Most groups are likely to evolve into more compact systems through HI-rich mergers.

Abstract

We present and explore the resolved atomic hydrogen (HI) content of 13 HI-rich and late-type dominated groups denoted `Choirs'. We quantify the HI content of the Choir galaxies with respect to the median of the HI-mass fraction ($f_{\textrm{HI}}$) of their grandparent HIPASS sample. We find that the HI mass fraction of the Choir galaxies is dispersed around the HIPASS median in the range $-1.4 \leq \Delta f_{\textrm{HI}}\textrm{[dex]}\leq 0.7$, from HI-excess to HI-deficient galaxy regime. The HI-excess/HI-deficient galaxies contain more/less than 2.5 times their expected HI content with respect to the HIPASS median. We show and discuss that the environmental processing in Choirs occurs via tidal stripping and galaxy mergers. Our analysis suggests that tidal stripping contributes to the loss of the HI, while galaxy mergers contribute to the enhancement of the HI. Exploring the mid-infrared properties of Choir galaxies we find possible environmental processing in only nine Choir galaxies, which indicates that environmental processing is more perceptible in the HI content than the mid-infrared properties. Moreover, we find that environmental processing occurs in Choir groups regardless of their global environment, whether they are in isolation or in proximity to the denser structures, such as cosmic web filaments. We explore possible scenarios of the Choirs evolution, taking into account their HI content, velocity dispersion, crossing time and their global environment. We conclude that the most likely evolution for the majority of Choir groups is that they will become more compact as their members undergo multiple HI-rich mergers.