Scylla. V. Constraints on the Spatial and Temporal Distribution of Bursts and the Interaction History of the Magellanic Clouds from Their Resolved Stellar Populations

Abstract We measure the star formation histories (SFHs) from the Scylla survey in ∼98,000 pc 2 and ∼75,000 pc 2 of the Small Magellanic Cloud (SMC) and Large Magellanic Cloud (LMC), respectively, using deep Hubble Space Telescope imaging (80% complete to > 1 mag below the ancient main-sequence turnoff, ∼25.1 and 26.0 mag in F475W and F814W) from 74 pointings. We group the fields into eight subregions in the SMC and seven in the LMC. We use the birth rate parameter to identify bursts of star formation and measure their properties in each subregion. Our methodology provides a standardized framework for burst identification and reveals both broad and fine burst characteristics. We identify global and local bursts, defined as those occurring in ≥half or <half of a galaxy’s subregions, respectively. In the SMC, we find two global (∼5 and 1.5 Gyr ago) and one local burst (∼3 Gyr ago). In the LMC, we find one global burst (∼3 Gyr ago). Comparing these findings with dynamical models of the LMC and SMC orbital histories, we find that when models predict a shared dynamical trigger for bursts across both galaxies, the burst begins earlier in the SMC with a greater enhancement in star formation rate than in the LMC. Finally, using age–metallicity relations and cumulative SFHs, we report that the Wing/Bridge region in the SMC resembles the southwestern LMC both chemically and in stellar mass assembly over the last ∼7 Gyr, possibly due to stellar material stripped from the LMC during their last interaction.