The chemical evolution of the LMC from APOGEE abundances: a hybrid two-infall OMEGA+ analysis

The Large Magellanic Cloud (LMC) provides resolved stellar abundances and star-formation histories that can be used together to test models of dwarf-galaxy chemical evolution. We investigated if the non-monotonic APOGEE [Mg/Fe] - [Fe/H] sequence can be explained by a hybrid history that combines a second gas-infall episode with a temporary increase in star-formation efficiency (SFE). We selected 4933 LMC red-giant-branch stars from APOGEE-2 DR17. We fitted an adaptively binned median Mg sequence with the two-zone open-box code OMEGA+. The formal fitting objective contained only the Mg sequence. The metallicity distribution function (MDF), one-dimensional abundance distributions, star-formation history (SFH), present-day mass partition, SFR, and supernova (SN) rate were retained as posterior diagnostics. The best-fitting model reproduces the Mg sequence with an RMS residual of 0.01 dex and also gives a close posterior match to O. It contains two delayed-tau infall episodes, with the second beginning at t 2=10.39 Gyr and with integrated mass ratio M 2/M 1=0.159, followed by a temporary Gaussian SFE enhancement centred at t=11.91 Gyr. The second infall is represented by a mixture of enriched and primordial gas. The model reproduces the timing of the late SFH enhancement and yields a present SFR within the adopted comparison range. A hybrid second-infall and SFE-enhancement history is a plausible scenario for reproducing the observed LMC Mg median sequence. Our fit explains the LMC evolution fairly well, but the remaining small MDF, mass, and SN-rate discrepancies suggest that a selection-function-aware treatment of the stellar distributions is required for a stricter comparison.