Neutral Hydrogen in the M96 Group: The Galaxies and the Intergalactic Ring

The M96 group is examined at 21 cm to study the galaxies' neutral hydrogen content and to search for evidence of interactions that might help explain the origin of the large intergalactic H I feature found there. M96, an Sab spiral, has 90% of its H I concentrated outside of the central bright optical disk--possibly captured intergalactic gas. The ringlike distribution of the intergalactic gas may, in turn, be shaped by interactions with M96. An extremely faint (B ~ -10 or -11) dwarf irregular galaxy was also found. Questions about the distance and membership of the M96 group are addressed, and it is shown that many previous group catalogs must be in error. A mass-to-light ratio of less than 30 is found for the M96 group; a number of previous estimates are inflated by inclusion of background galaxies--a problem that may be widespread in group studies. In the appendix, it is shown that a hexagonal (or "honeycomb") observing grid yields more optimized spatial frequency coverage than a rectangular grid.