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ABSTRACT  We study the metallicities and abundance ratios of early‐type galaxies in cosmological semi‐analytic models (SAMs) within the hierarchical galaxy formation paradigm. To achieve this we implemented a detailed galactic chemical evolution model and can now predict abundances of individual elements for the galaxies in the semi‐analytic simulations. This is the first time a SAM with feedback from active galactic nuclei has included a chemical evolution prescription that relaxes the instantaneous recycling approximation. We find that the new models are able to reproduce the observed mass–metallicity  ( M  ★ –[ Z /H])  relation and, for the first time in a SAM, we reproduce the observed positive slope of the mass–abundance ratio  ( M  ★ –[α/Fe])  relation. Our results indicate that in order to simultaneously match these observations of early‐type galaxies, the use of both a very mildly top‐heavy initial mass function (i.e. with a slope of   x = 1.15  as opposed to a standard   x = 1.3 ), and a lower fraction of binaries that explode as Type Ia supernovae (SNe Ia) appears to be required. We also examine the rate of SN explosions in the simulated galaxies. In early‐type (non‐star‐forming) galaxies, our predictions are also consistent with the observed SNe rates. However, in star‐forming galaxies, a higher fraction of SN Ia binaries than in our preferred model is required to match the data. If, however, we deviate from the classical model and introduce a population of SNe Ia with very short delay times, our models simultaneously produce a good match to the observed metallicities, abundance ratios and SN rates.

Galactic chemical evolution in hierarchical formation models – I. Early‐type galaxies in the local Universe