Chemical evolution of the bulge of M31: Predictions about abundance ratios

We aim to reproduce the chemical evolution of the bulge ofM31 using a detailed chemical evolution model, including radial gas flows coming from the disc.We study the impact of the initial mass function, the star formation rate and the time-scale for bulge formation on the metallicity distribution function of stars. We compute several models of chemical evolution using the metallicity distribution of dwarf stars as an observational constraint for the bulge of M31. Then, using the model that best reproduces the metallicity distribution function, we predict the [X/Fe] versus [Fe/H] relations for several chemical elements (O, Mg, Si, Ca, C, N). Our best model for the bulge of M31 is obtained by using a robust statistical method and assumes a Salpeter initial mass function, a Schmidt–Kennicutt law for star formation with an exponent k = 1.5, an efficiency of star formation of∼15±0.27 Gyr−1 and an infall time-scale of∼0.10±0.03 Gyr. Our results suggest that the bulge of M31 formed very quickly as a result of an intense star formation rate and an initial mass function flatter than in the solar vicinity but similar to that inferred for the Milky Way bulge. The [α/Fe] ratios in the stars of the bulge of M31 should be high for most of the [Fe/H] range, as observed in the Milky Way bulge. These predictions await future data to be proven.