it is widely known that elliptical galaxies have little or no gas, but how is this determined? What is the amount of gas? Is there a decent ratio of stellar mass to gas for ellipticals? How does this vary between normal ellipticals and those that were formed by mergers (or still look like merger remnants)? Thanks for your help!
There is an ongoing survey of molecular gas in elliptical galaxies, and the first results are summarized in The ATLAS3D project - IV. The molecular gas content of early-type galaxies.
Some key points: