Mapping HI 21-cm in the Klemola 31 group at z = 0.029: emission and absorption towards PKS2020-370

TL;DR

This study uses MeerKAT observations to map HI gas in the Klemola 31 galaxy group, revealing emission, absorption features, and complex gas dynamics, including interactions and possible ram-pressure stripping effects.

Contribution

First detailed HI emission and absorption mapping of the Klemola 31 group, analyzing gas properties and dynamics with models and multi-phase gas indicators.

Findings

Detected four galaxies in HI emission and absorption towards PKS2020-370.

Identified high spin temperature and potential extra-planar gas in Klemola31A.

Observed galaxy interactions, tidal tails, and ram-pressure stripping effects.

Abstract

We present MeerKAT Absorption Line Survey (MALS) observations of the HI gas in the Klemola31 galaxy group ($z=0.029$), located along the line of sight to the radio-loud quasar PKS2020-370 ($z=1.048$). Four galaxies of the group are detected in HI emission, and HI absorption is also detected in front of PKS2020-370 in Klemola31A. The emission and absorption are somewhat compensating on the line of sight of the quasar, and the derived column density of the absorption appears under-estimated, with respect to the neighbouring emission. A symmetric tilted-ring model of Klemola31A, assuming the absorbing gas in regular rotation in the plane, yields a rather high spin temperature of 530K. An alternative interpretation is that the absorbing gas is extra-planar, which will also account for its non-circular motion. The NaI/CaII ratio also suggests that the absorbing gas is unrelated to cold HI disk. Two of the galaxies in the Klemola group are interacting with a small companion, and reveal typical tidal tails, and velocity perturbations. Only one of the galaxies, ESO400-13, reveals a strong HI deficiency, and a characteristic ram-pressure stripping, with a total asymmetry in the distribution of its gas. Since a small galaxy group as Klemola31 is not expected to host a dense intra-group gas, this galaxy must be crossing the group at a very high velocity, mostly in the sky plane.