Chemical abundances in clusters of galaxies

We study the origin of iron and α-elements (O, Mg, Si) in clusters of galaxies. In particular, we discuss the [O/Fe] ratio and the iron mass-to-luminosity ratio in the intracluster medium (ICM) and their link to the chemical and dynamical evolution of elliptical and lenticular galaxies. We adopt a detailed model of galactic evolution incorporating the development of supernovae-driven galactic winds which pollute the ICM with enriched ejecta. We demonstrate quantitatively, after David et al. (1991), the crucial dependence upon the assumed stellar initial mass function in determining the evolution of the mass and abundances ratios of heavy elements in typical model ICMs. We show that completely opposite behaviours of [α/Fe] ratios (i.e. positive versus negative ratios) can be obtained by varying the initial mass function without altering the classic assumptions regarding type Ia supernovae progenitors or their nucleosynthesis. Our results indicate that models incorporating somewhat flatter-than-Salpeter initial mass functions (i.e. x=~1, as opposed to x=1.35) are preferred, provided the intracluster medium iron mass-to-luminosity ratio, preliminary [α/Fe]>0 ASCA results, and present-day type Ia supernovae rates, are to be matched. A simple Virgo cluster simulation which adheres to these constraints shows that ~70% of the measured ICM iron mass has its origin in type II supernovae, with the remainder being synthesized in type Ia systems.