Exploring the Origin of the Distance Bimodality of Stars in the Periphery of the Small Magellanic Cloud with APOGEE and Gaia

TL;DR

This study investigates the origin of the distance bimodality of stars in the Small Magellanic Cloud's periphery using Gaia and APOGEE data, revealing tidal interactions with the Large Magellanic Cloud as a key factor.

Contribution

It provides a detailed kinematic and chemical analysis of the bimodal stellar populations, linking them to tidal effects from the LMC.

Findings

Near stars are approaching us, indicating tidal stripping from the SMC center.

Far stars have metallicity similar to western periphery, suggesting different origins.

Bimodality is likely caused by tidal interactions with the LMC.

Abstract

The Magellanic Cloud system represents a unique laboratory for study of both interacting dwarf galaxies and the ongoing process of the formation of the Milky Way and its halo. We focus on one aspect of this complex, 3 body interaction - the dynamical perturbation of the Small Magellanic Cloud (SMC) by the Large Magellanic Cloud (LMC), and specifically potential tidal effects on the SMC's eastern side. Using Gaia astrometry and the precise radial velocities and multi-element chemical abundances from APOGEE-2 DR17, we explore the well-known distance bimodality on the eastern side of the SMC. Through estimated stellar distances, proper motions, and radial velocities, we characterize the kinematics of the two populations in the bimodality and compare their properties with those of SMC populations elsewhere. Moreover, while all regions explored by APOGEE seem to show a single chemical enrichment history, the metallicity distribution function (MDF), of the "far" stars on the eastern periphery of the SMC is found to resemble that for the more metal-poor fields of the western periphery, whereas the MDF for the "near" stars on the eastern periphery resembles that for stars in the SMC center. The closer eastern periphery stars also show radial velocities (corrected for SMC rotation and bulk motion) that are, on average, approaching us relative to all other SMC populations sampled. We interpret these trends as evidence that the near stars on the eastern side of the SMC represent material pulled out of the central SMC as part of its tidal interaction with the LMC.