Mapping H i 21-cm in the Klemola 31 group at z = 0.029: emission and absorption towards PKS 2020-370
Résumé
We present MeerKAT Absorption Line Survey (MALS) observations of the H i gas in the Klemola 31 galaxy group (z = 0.029), located along the line of sight to the radio-loud quasar PKS 2020-370 (z = 1.048). Four galaxies of the group are detected in H i emission, and H i absorption is also detected in front of PKS 2020-370 in Klemola 31A. The emission and absorption are somewhat compensating on the line of sight of the quasar, and the derived column density of the absorption appears underestimated , with respect to the neighbouring emission. A symmetric tilted-ring model of Klemola 31A, assuming the absorbing gas in regular rotation in the plane, yields a rather high spin temperature of 530 K. An alternative interpretation is that the absorbing gas is extra-planar, which will also account for its non-circular motion. The Na i/Ca ii ratio also suggests that the absorbing gas is unrelated to cold H i 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, ESO 400-13, reveals a strong H i deficiency, and a characteristic ram-pressure stripping, with a total asymmetry in the distribution of its gas. Since a small galaxy group as Klemola 31 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.
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