DWARF GALAXIES AND THE ORIGIN OF THE INTRACLUSTER MEDIUM

Following the recent suggestion that it is dwarf galaxies in clusters- as opposed to large ellipticals-that provide the intracluster gas, we estimate the metallicity of the intracluster medium in such a case. We derive analytical expressions for the fraction of mass of dwarf galax ies that is ejected and estimate the metallicity of the resulting intr acluster gas. We find that the metallicity resulting from this hypothe sis is adequate only for clusters with low-metallicity gas. Since gala ctic winds from dwarf galaxies occur much earlier than those from elli pticals, because of the smaller binding energy of the gas, we show tha t the gas ejected by dwarf galaxies is enriched mostly by Type II supe rnovae, as opposed to Type I supernovae in the case of large galaxies. We further point out that the gas in small-scale structures, which ne ver cools and forms stars owing to low temperatures and, consequently, a large cooling timescale, gets dispersed in the process of hierarchi cal clustering and is incorporated as the diffuse intracluster gas. We show that this process can provide enough hot gas to be compatible wi th X-ray observations in rich clusters.