Prevalence of neutral gas in centres of merging galaxies-II: nuclear H I and multiwavelength properties

Abstract

Using a sample of 38 radio-loud galaxy mergers at z ≤ 0.2, we confirm the high detection rate (∼84 per cent) of H I 21-cm absorption in mergers, which is significantly higher (∼4 times) than in non-mergers. The distributions of the H I column density [N({H I})] 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 H I gas with various multiwavelength properties of the mergers. While the inferred N({H I}) and gas kinematics do not show strong (i.e. ≥3σ level) correlation with galaxy properties, we find that the incidence and N({H I}) 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({H I}) and line width of H I absorption increase from the pre-merger to the post-merger stages. The 100 per cent 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.