Modelling element abundances in semi-analytic models of galaxy formation

We update the treatment of chemical evolution in the Munich semi-analytic model, L-GALAXIES. Our new implementation includes delayed enrichment from stellar winds, Type II supernovae (SNe-II) and Type Ia supernovae (SNe-Ia), as well as metallicity-dependent yields and a reformulation of the associated supernova feedback. Two different sets of SN-II yields and three different SN-Ia delay-time distributions (DTDs) are considered, and 11 heavy elements (including O, Mg and Fe) are self-consistently tracked. We compare the results of this new implementation with data on (a) local, star-forming galaxies, (b) Milky Way disc G dwarfs and (c) local, elliptical galaxies. We find that the z = 0 gas-phase mass-metallicity relation is very well reproduced for all forms of DTD considered, as is the [Fe/H] distribution in the Milky Way disc. The [O/Fe] distribution in the Milky Way disc is best reproduced when using a DTD with ≤50 per cent of SNe-Ia exploding within ∼400 Myr. Positive slopes in the mass-[α/Fe] relations of local ellipticals are also obtained when using a DTD with such a minor `prompt' component. Alternatively, metal-rich winds that drive light α elements directly out into the circumgalactic medium also produce positive slopes for all forms of DTD and SN-II yields considered. Overall, we find that the best model for matching the wide range of observational data considered here should include a power-law SN-Ia DTD, SN-II yields that take account of prior mass-loss through stellar winds and some direct ejection of light α elements out of galaxies.