Testing the universal stellar IMF on the metallicity distribution in the bulges of the Milky Way and M 31

Aims. We test whether the universal initial mass function (UIMF) or the integrated galaxial IMF (IGIMF) can be employed to explain the metallicity distribution ( MD) of giants in the Galactic bulge. Methods. We make use of a single-zone chemical evolution model developed for the Milky Way bulge in the context of an inside-out model for the formation of the Galaxy. We checked whether it is possible to constrain the yields above 80 M-circle dot by forcing the UIMF and required that the resulting MD matches the observed ones. We also extended the analysis to the bulge of M 31 to investigate a possible variation of the IMF among galactic bulges. Several parameters that have an impact on stellar evolution (star-formation efficiency, gas infall timescale) are varied. Results. We show that it is not possible to satisfactorily reproduce the observed metallicity distribution in the two galactic bulges unless assuming a flatter IMF ( x <= 1.1) than the universal one. Conclusions. We conlude that it is necessary to assume a variation in the IMF among the various environments.