Unraveling the kinematic and morphological evolution of the Small Magellanic Cloud

We modeled the kinematics of the Small Magellanic Cloud (SMC) by analyzing the proper motion (PM) from Gaia DR3 of nine different stellar populations, which include young main sequence (MS) stars (< 2 Gyr), red giant branch stars, red clump stars, red giants with line-of-sight velocities, and three groups of star clusters. This analysis was carried out using a robust Markov Chain Monte Carlo method to derive up to 7 kinematic parameters. We trace the evolution from a non-rotating flattened elliptical system as mapped by the old population to a rotating highly stretched disk structure as denoted by the young MS stars and clusters (< 400 Myr). We estimated that the inclination, i (~ 58$^\circ$ to 82$^\circ$) decreases and the position angle, $\Theta$ (~ 180$^\circ$ to 240$^\circ$) increases with age. We estimated an asymptotic velocity of ~ 49 - 89 km s$^{-1}$ with scale-radius of ~ 6 - 9 kpc for the young MS populations with velocity dispersion of ~ 11 km s$^{-1}$, suggesting a rotation-supported disk structure. Our models estimate a line-of-sight extension of ~ 30 kpc, in agreement with observations. We identified four regions of the SMC showing anomalies in the residual PM, the East Anomaly (EA), South East Anomaly (SEA), South Anomaly (SA), and West Anomaly (WA). The SEA appears like an infalling feature and is identified for the first time. The tidal imprints observed in the residual PM of the SMC suggest that its evolution is considerably shaped by the recent interaction with the Large Magellanic Cloud.
Comment: Accepted for publication in ApJ. 18 pages, 13 figures, 2 tables