Disturbed, diffuse, or just missing? A global study of the HI content of Hickson Compact Groups by M. G. Jones et al. on Wednesday 30 November

Hickson Compact Groups (HCGs) are dense configurations of 4 to 10 galaxies,

whose HI (neutral gas) morphology appears to follow an evolutionary sequence of

three phases, with gas initially confined to galaxies, then significant amounts

spread throughout the intra-group medium, and finally with almost no gas

remaining in the galaxies themselves. The HI deficiency of HCGs is expected to

increase as the HI morphological phase progresses along this sequence,

potentially making it a useful proxy for evolutionary phase. We test this

hypothesis for the first time with a large sample of 38 HCGs with VLA HI

observations that are uniformly reduced and analysed with a purpose-built

pipeline. However, we find little evidence that HI deficiency can be used as a

proxy for the evolutionary phase of a HCG in either of the first two phases,

with the distribution of HI deficiency being consistent in both, although it

does greatly increase in the third phase. This appears to be the result to

three factors: a) there is already a broad range of HI deficiencies in Phase 1

HCGs, possibly due to their differing locations relative to large scale

structures; b) the timescale for major interactions and morphological changes

is, in general, considerably shorter than the timescale for the destruction or

consumption of HI gas; and c) some groups have their HI content rejuvenated by

the late addition of a new gas-rich member (for which we added a new sub-phase,

3c, to the established evolutionary sequence). Finally, across all HCGs

studied, we identify only a few cases where there is strong evidence for the

existence of a previously proposed diffuse HI component in the intra-group

medium, which might be detectable with improved observations. This work was

completed with considerable attention paid to scientific reproducibility, and

all reduction and analysis has been made public via Github and Zenodo.

(Abridged)

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.15687v1