Abundance ratios in hierarchical galaxy formation

In models of hierarchical galaxy formation ellipticals form through the merging of smaller disk systems (e.g., Kauffmann, White and Guiderdoni,1993). Such models predict that galaxies in low-density environments form later than their counterparts in clusters, and more massive galaxies form later (Kauffmann, 1996). Here we present simulations based on semi-analytic models that include the chemical enrichment of the elements magnesium andiron. The chemical evolution code is described in Thomas, Greggio and Bender(1998, 1999). The results are: 1) The Mg/Fe predicted for elliptical galaxies does not agree with the values derived from observations. 2) The most luminous (and massive) ellipticals have the lowest Mg/Fe, in conflict with the observational evidence. 3) Galaxies in looser environments exhibit lower Mg/Fe ratios. 4) Bulges are most α-enhanced independent of the environment. For more details I refer the reader to Thomas (1999) and Thomas and Kauffmann (1999).