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Infall Models of Elliptical Galaxies: Further Evidence for a Top-Heavy Initial Mass Function

Chemical and photometric models of elliptical galaxies with infall of primordial gas, and subsequent ejection of processed material via galactic winds, are described. Ensuring that these models are consistent with the present-day colour-luminosity relation and the measured intracluster medium (ICM) abundances, we demonstrate that the initial mass function (IMF) must be significantly flatter (i.e., x<=0.80) than the canonical Salpeter slope (i.e., x=1.35). Such a ``top-heavy'' IMF is in agreement with the earlier conclusions based upon closed-box models for elliptical galaxy evolution. On the other hand, the top-heavy IMF, in conjunction with these semi-analytic infall models, predicts an ICM gas mass which exceeds that observed by up to a factor three, in contrast with the canonical closed-box models. Time and position-dependent IMF formalisms may prove to be a fruitful avenue for future research, but those presently available in the literature are shown to be inconsistent with several important observational constraints.