Cooling Flows and Metallicity Gradients in Clusters of Galaxies

The X-ray emission by hot gas at the centers of clusters of galaxies iscommonly modeled assuming the existence of steady-state, inhomogeneous coolingflows. We derive the metallicity profiles of the intracluster medium expectedfrom such models. The inflowing gas is chemically enriched by type Iasupernovae and stellar mass loss in the outer parts of the central galaxy,which may give rise to a substantial metallicity gradient. The amplitude of theexpected metallicity enhancement towards the cluster center is proportional tothe ratio of the central galaxy luminosity to the mass inflow rate. Themetallicity of the hotter phases is expected to be higher than that of thecolder, denser phases. The metallicity profile expected for the Centauruscluster is in good agreement with the metallicity gradient recently inferredfrom ASCA measurements (Fukazawa et al. 1994). However, current data do notrule out alternative models where cooling is balanced by some heat source. Themetallicity gradient does not need to be present in all clusters, depending onthe recent merging history of the gas around the central cluster galaxy, and onthe ratio of the stellar mass in the central galaxy to the gas mass in thecooling flow.Comment: uuencoded postscript, 8 pages of text + 2 figures, accepted by The Astrophysical Journal (Letters