Star Formation Histories in Early-type Galaxies

I discuss the formation of α-enhanced metal-rich stellar populations in the nuclei of luminous ellipticals. Based on hierarchical clustering , different galaxy formation scenarios, which imply different star formation histories, are considered. In contrast to the fast clumpy collapse mode, the late merger of two spiral galaxies fails to reproduce significantly α-enhanced abundance ratios, unless the IMF is flattened. Following the star formation history predicted by semi-analytic models of hierarchical clustering for the average elliptical, solar abundance ratios are obtained with Salpeter IMF. According to the models, bright ellipticals in the field are expected to have significantly lower Mg/Fe ratios than their counterparts in a cluster.