We present a new scenario in which massive intragroup H i clouds are the high-density parts of large H i rings/arcs formed by dynamical interaction between galaxy groups and gas-rich, low surface brightness (LSB) galaxies with extended gas discs. Our hydrodynamical simulations demonstrate that the group tidal field is very efficient at stripping the outer H i gas of the disc if the gaseous disc of the LSB galaxy extends 2–5 times further than the stellar disc. We find that a massive, extended ‘leading stream’ orbiting the centre of the group can form out of the stripped outer H i envelope, while the severely shrunken LSB galaxy, whose stellar disc remains unaffected, continues on its path. The result is a relatively isolated, massive H i cloud with a ring- or arc-like shape, a very inhomogeneous density distribution (NH i∼ 1.0 × 1017–1.1 × 1020 atom cm−2), and, initially, no stellar content. Only the high-density peaks of the simulated intragroup H i ring/arc can be detected in many current H i observations. These will appear as relatively isolated ‘H i islands’ near the group centre. We also find that star formation can occur within the ring/arc, if the total gas mass within the intragroup ring/arc is very large (∼4 × 109 M⊙). We discuss these results in terms of existing observations of intragroup gas (e.g. the Leo Ring and HIPASS J0731–69) and intergalactic H ii regions.
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Bekki et al. (2005) studied this question.