COOL DENSE GAS IN EARLY-TYPE GALAXIES

CO observations have shown that many lenticular and elliptical galaxie s contain significant amounts of cool dense gas. This review summarize s the observational results related to the neutral gas phase and prese nts a systematic comparison with other interstellar and stellar data. The discovery of very dense molecular gas in the nuclear regions of ea rly-type galaxies, the possible existence of a dust component neither seen optically nor in CO, internal inconsistencies of cooling flow sce narios, the origin of the cool gas, the presence of massive stars, asp ects of galaxy evolution, and possibilities for future research are di scussed in the light of the new data.