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-phasemetallicity (Z(g)) and stellarmetallicity (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 similar to 2-3. A direct CGM enrichment fraction of similar to 90 per cent for SNe-II is preferred. We find that massive disc galaxies have slightly flatter Z(g) 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 Z(g) profile slope is also seen in our MaNGA-DR15 sample of 571 star-forming disc galaxies, although below log(10)(M-*/M-circle dot) similar to 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 25M(circle dot), reflecting recent theoretical and observational estimates, can also provide a good match to observed Z(g) and Z(*) profiles at z = 0 in L-GALAXIES 2020. However, this model version fails to reproduce an evolution in Z(g) at fixed mass over cosmic time, or the magnesium abundances observed in the intracluster medium (ICM).

Automated summary

The modified version of the L-GALAXIES 2020 model introduces increased direct metal enrichment of the circumgalactic medium by supernovae, enabling it to reproduce observed gas-phase and stellar metallicity radial profiles, mass-metallicity relations, and their evolution. The model also shows differences in metallicity distribution between high-mass and low-mass disc galaxies, potentially due to enrichment mechanisms and accretion. However, the model struggles to replicate the evolution of metallicity over cosmic time and magnesium abundances in the intracluster medium.