MOLECULAR GAS IN ELLIPTIC GALAXIES - CO OBSERVATIONS OF AN IRAS FLUX-LIMITED SAMPLE

A search for CO(2-1) emission from 42 early-type galaxies with 100 mu m flux densities greater than 1 Jy detected (tentatively in some cases ) 11 galaxies and tentatively found absorption against the active nucl eus in two. Data from this survey and from the literature show that th e overall detection rate of CO emission or absorption in elliptical ga laxies is 45% and that the detection rate increases with increasing 10 0 mu m flux density. The data suggest that all elliptical galaxies con tain a small amount of cold interstellar matter. The CO and far-infrar ed fluxes are well correlated, though the relationship shows a lot of scatter, which does not appear to be caused by variations in the tempe rature of the interstellar dust and probably indicates differences in the physical state of the interstellar medium from galaxy to galaxy. T he CO flux densities are completely uncorrelated with the galactic sta rlight. The detection of CO emission shows that many elliptical galaxi es have dense cold gas in their inner regions. The four galaxies which are known to have CO absorption, including the two from the present p aper, have relatively narrow absorption components which are at the ga laxy's systemic velocity and/or redshifted with respect to this veloci ty, consistent with infall to the center of the galaxy.