The chemical evolution of the Large Magellanic Cloud from APOGEE abundances: A hybrid two-infall OMEGA+ analysis

The Large Magellanic Cloud (LMC) provides resolved stellar abundances and star formation histories (SFHs) 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 . The formal fitting objective contained only the Mg sequence. The metallicity distribution function (MDF), one-dimensional abundance distributions, SFH, present-day mass partition, star formation rate (SFR), and supernova (SN) rate were retained as posterior diagnostics. OMEGA+ The best-fitting model reproduces the Mg sequence with a root mean square (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 an integrated mass ratio of M_2/M_1=0.159, followed by a temporary Gaussian SFE enhancement centered 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.