Timescales for Galaxy Formation and Intra-Cluster Medium Enrichment
Recent observations with ASCA (Mushotzky 94, New Horizon of X-Ray Astron.-1st Results from ASCA) have confirmed the prediction (Arnaud et al. 92, A&A 254, 49; Elbaz et al. 95, to appear in A&A) that the Fe present in the intra-cluster medium (ICM) is mainly due to SNII and not SNIa: α-elements (O, Ne, Si, S) are overabundant with respect to Fe. To account for the large Fe mass present in galaxy clusters as well as these abundances ratios, one must consider that the IMF was different in the past, favouring high-mass stars. Moreover, the simplest way to eject the enriched ISM into the ICM is to consider that the same high-mass stars that were responsible for the Fe enrichment have also driven a galactic wind in young E/SO’s.