Thursday

The close proximity of the Magellanic Clouds (MCs) to us makes it possible to obtain 3D velocities for a statistically significant stellar sample, paving the way for an accurate study of the timing and nature of the encounters between such galaxies. In order to study the interactions between the MCs, we need to first understand their inner structure, an undertaking that has proven to be puzzling, especially for the case of the Small Magellanic Cloud (SMC). The stellar content of the SMC, which hosts the smaller dark matter mass of the MCs, is prone to strong tidal forces. This, combined with the repeated interactions between the SMC and its larger companion, the Large Magellanic Cloud (LMC), have created a very complex structure that has bewildered the community for decades.

To shed light on these aspects, I present here a comprehensive study of the SMC that includes the 3D structure and the quantitative star formation history (SFH). I use deep colour-magnitude diagrams (CMDs) from the Survey of the MAgellanic Stellar History (SMASH) combined with proper motions from Gaia EDR3 to study the red clump stars and to constrain SMC 3D structure. SMASH CMDs are compared to synthetic ones via a genetic algorithm; this allows me to produce the most accurate quantitative SFH of the SMC. We find that tidal interactions between the two galaxies have played a crucial role in the evolution of its stellar populations for the last 3.5 Gyr, including a likely close encounter ≃ 2 Gyr ago. These results set important constraints on the timing of LMC-SMC collisions, as well as on the physics behind star formation induced by tidal encounters.