The Role of a Hot Gas Environment in the Evolution of Galaxies

Most spiral galaxies are found in galaxy groups with low velocitydispersions; most E/S0 galaxies are found in galaxy groups with relatively highvelocity dispersions. The mass of the hot gas we can observe in the E/S0 groupsvia their thermal X-ray emission is, on average, as much as the baryonic massof the galaxies in these groups. By comparison, galaxy clusters have as much ormore hot gas than stellar mass. Hot gas in S-rich groups, however, is of lowenough temperature for its X-ray emission to suffer heavy absorption due toGalactic HI and related observational effects, and hence is hard to detect. Wepostulate that such lower temperature hot gas does exist in low velocitydispersion, S-rich groups, and explore the consequences of this assumption. Fora wide range of metallicity and density, hot gas in S-rich groups can cool infar less than a Hubble time. If such gas exists and can cool, especially wheninteracting with HI in existing galaxies, then it can help link together anumber of disparate observations, both Galactic and extragalactic, that areotherwise difficult to understand.Comment: 16 pages with one figure. ApJ Letters, in pres