A tale of two galaxies: H i rich and poor in the star-forming J1051−17 galaxy group

We report on multi-wavelength observations of the HIPASS J1051−17 galaxy group. Narrow-band Hα imaging revealed the original HIPASS H i source to be a galaxy group with at least 9 members, follow-up DEIMOS spectroscopy from Keck confirmed five new dwarf galaxies near the group, while six additional galaxies are confirmed by radial velocity matching in the surrounding field. We find no evidence of tidal dwarf galaxies in this group. One intriguing aspect of this galaxy group is the presence of two spiral galaxies in close proximity and of a similar stellar mass, but with vastly different H i masses. The H i-excess spiral is a polar ring galaxy with extended spiral arms, and the H i-deficient spiral is a more compact, high surface brightness galaxy with potentially up to ≈ 3 × higher star formation rate. The existence of two such spiral galaxies in the same environment shines a light on the internal processes governing galaxy formation, and highlights the importance of angular momentum on the star formation properties of galaxies. Such a detailed study illustrates the need to understand the physical processes in groups that give rise to the various scaling relations we observe.