THE COOL INTERSTELLAR MEDIUM IN ELLIPTICAL GALAXIES. II. GAS CONTENT IN THE VOLUME-LIMITED SAMPLE AND RESULTS FROM THE COMBINED ELLIPTICAL AND LENTICULAR SURVEYS

Abstract

We report new observations of atomic and molecular gas in a volume limited\nsample of elliptical galaxies. Combining the elliptical sample with an earlier\nand similar lenticular one, we show that cool gas detection rates are very\nsimilar among low luminosity E and SO galaxies but are much higher among\nluminous S0s. Using the combined sample we revisit the correlation between cool\ngas mass and blue luminosity which emerged from our lenticular survey, finding\nstrong support for previous claims that the molecular gas in ellipticals and\nlenticulars has different origins. Unexpectedly, however, and contrary to\nearlier claims, the same is not true for atomic gas. We speculate that both the\nAGN feedback and merger paradigms might offer explanations for differences in\ndetection rates, and might also point towards an understanding of why the two\ngas phases could follow different evolutionary paths in Es and S0s. Finally we\npresent a new and puzzling discovery concerning the global mix of atomic and\nmolecular gas in early type galaxies. Atomic gas comprises a greater fraction\nof the cool ISM in more gas rich galaxies, a trend which can be plausibly\nexplained. The puzzle is that galaxies tend to cluster around\nmolecular-to-atomic gas mass ratios near either 0.05 or 0.5.\n