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

We present a modified version of the L-galaxies2020 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-galaxies2020 model is able to simultaneously reproduce the gas-phase metallicity ($Z_{\rm {g}}$) 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 $Z_{\rm {g}}$ profiles than their lower-mass counterparts in L-galaxies2020, 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 $Z_{\rm {g}}$ 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 $25\, {\rm M}_{\odot }$, reflecting recent theoretical and observational estimates, can also provide a good match to observed $Z_{\rm {g}}$ and Z* profiles at z = 0 in L-galaxies2020. However, this model version fails to reproduce an evolution in $Z_{\rm {g}}$ at fixed mass over cosmic time, or the magnesium abundances observed in the intracluster medium (ICM).