L-GALAXIES 2020: the evolution of radial metallicity profiles and global metallicities in disc galaxies

We present a modified version of the L-GALAXIES 2020 semi-analytic model of galaxy evolution, which includes significantly increased direct metal enrichment of the circumgalactic medium (CGM) by supernovae (SNe). These more metal-rich outflows do not require increased mass-loading factors, in contrast to some other galaxy evolution models. This modified L-GALAXIES 2020 model is able to simultaneously reproduce the gas-phase metallicity (Zg) and stellar metallicity (Z*) radial profiles observed in nearby disc galaxies by MaNGA and MUSE, as well as the observed mass - metallicity relations for gas and stars at z = 0 and their evolution back to z ~ 2 - 3. A direct CGM enrichment fraction of ~90 per cent for SNe-II is preferred. We find that massive disc galaxies have slightly flatter Zg profiles than their lower-mass counterparts in L-GALAXIES 2020, due to more efficient enrichment of their outskirts via inside-out growth and metal-rich accretion. Such a weak, positive correlation between stellar mass and Zg profile slope is also seen in our MaNGA-DR15 sample of 571 star-forming disc galaxies, although below log10(M*/M?)~10.0 this observational result is strongly dependent on the metallicity diagnostic and morphological selection chosen. In addition, a lowered maximum SN-II progenitor mass of 25 M?, reflecting recent theoretical and observational estimates, can also provide a good match to observed Zg and Z* profiles at z = 0 in L-GALAXIES 2020. However, this model version fails to reproduce an evolution in Zg at fixed mass over cosmic time, or the magnesium abundances observed in the intracluster medium (ICM).