# Prevalence of neutral gas in centres of merging galaxies-II: nuclear HI and multi-wavelength properties

## TL;DR

This study reveals a high prevalence of nuclear HI gas in merging galaxies, with increased detection rates and gas properties evolving through merger stages, highlighting the resilience of neutral gas during galaxy coalescence.

## Contribution

It provides the first comprehensive analysis of nuclear HI absorption in a large sample of merging galaxies, demonstrating higher detection rates and evolving gas properties compared to non-mergers.

## Key findings

- High HI detection rate (~84%) in mergers
- HI properties vary with merger stage
- Neutral gas persists through coalescence

## Abstract

Using a sample of 38 radio-loud galaxy mergers at z<=0.2, we confirm the high detection rate (~84%) of HI 21-cm absorption in mergers, which is significantly higher (~4 times) than in non-mergers. The distributions of the HI column density [N(HI)] and velocity shift of the absorption with respect to the systemic redshift of the galaxy hosting the radio source in mergers are significantly different from that in non-mergers. We investigate the connection of the nuclear HI gas with various multi-wavelength properties of the mergers. While the inferred N(HI) and gas kinematics do not show strong (i.e. >=3-sigma level) correlation with galaxy properties, we find that the incidence and N(HI) of absorption tend to be slightly higher at smaller projected separations between the galaxy pairs and among the lower stellar mass-radio galaxies. The incidence, N(HI) and line width of HI absorption increase from the pre-merger to the post-merger stages. The 100% detection rate in post-mergers indicates that the neutral gas in the circumnuclear regions survives the coalescence period and is not yet quenched by the nuclear radio activity.