Cold Gas and Star Formation in Elliptical Galaxies
  Elliptical galaxies outside dense clusters are observed to contain small amounts (relative to spiral galaxies) of cold interstellar gas. This review discusses the atomic gas, the molecular gas, and the dust in elliptical galaxies. Field elliptical galaxies contain about 0.01 to 0.1 of the cold interstellar matter content of spiral galaxies of similar luminosity, and support a low level of star formation. The surface densities of cold gas clouds in the centers of some elliptical galaxies are comparable to those in the densest regions of the Galactic disk. These observations suggest that elliptical galaxies in the field, like spiral galaxies, have a long-lived interstellar medium which evolves with the galaxy. The timescale for star formation, however, appears to be much shorter, leaving these systems with little gas at the present epoch. 
G. R. Knapp