Stellar Birth Radii in the LMC: Insights into Chemodynamics, Radial Migration, and Star Formation across the Disk

Abstract

The LMC and SMC are interacting dwarf galaxies offering a valuable testbed for studying galactic mergers. We investigate the LMC’s chemodynamic history during its interaction with the SMC by inferring stellar birth radii using APOGEE DR17 data, first validated on a hydrodynamical simulation reproducing their interaction history. Using birth radii and stellar ages, we identify signatures of dynamical and chemical evolution across the LMC disk. The LMC’s metallicity gradient steepened around 5, 3, and 1 Gyr ago, coinciding with enhanced star formation (SF). These events show distinct spatial patterns—initially inner-disk concentrated 5 Gyr ago, expanding outward by 3 Gyr, and becoming widespread with renewed central activity at 1 Gyr—likely reflecting changes in spin alignment if SF enhancements track the SMC’s pericenter passages. After accounting for disk scale-length differences, inferred radial migration strength rises relative to Milky Way (MW) expectations at ages <5 Gyr and during major SF enhancements reported in the literature. The most α-enriched stars formed 2–3 Gyr ago at birth radii of 2–4 kpc, the only epoch when SF was broadly distributed. Unlike the MW, the LMC lacks a clear [α/M]-[Fe/H] bimodality, likely due to more centrally concentrated SF versus the MW’s extended outer-disk SF. These results strongly constrain the LMC’s assembly and its interaction with the SMC.