1995A&A...297..643W

A survey of CO emission in 29 far-IR selected elliptical galaxies resulted in 16 detections, of which 3 remain tentative. The molecular gas masses range from 2x10⁶M_☉ to 1x10⁹M_☉, and appear to be unrelated to the underlying stellar population. This suggests an external origin of the gas. Most of the elliptical galaxies with a molecular gas component have a gas-to-dust mass ratio of ∼700, where dust masses are derived from the IRAS fluxes, but some appear to have a ratio as low as 50. A small apparent gas-to-dust mass ratio is also found for some late-type galaxies, and is correlated with a low dust temperature. We suggest that a large part of the far-infrared emission from these galaxies (both early- and late-types) comes from dust associated with the atomic gas component rather than star forming regions associated with the molecular gas, and that they contain a cold dust component. Low excitation temperatures for CO transitions in galaxies with cold dust could lead to an underestimate of the molecular gas mass by a factor of 5. The average M_H2/M_HI ratio for the elliptical galaxies is 2-5 times lower than for normal spiral galaxies. Field ellipticals appear more likely to contain an observable molecular gas component than those ellipticals residing in groups and clusters.