The VMC survey -- XLI. Stellar proper motions within the Small Magellanic Cloud

TL;DR

This study measures stellar proper motions in the Small Magellanic Cloud using near-infrared VISTA data, revealing internal kinematics and interactions with the Magellanic Bridge and other structures.

Contribution

First detailed internal kinematic analysis of SMC stellar populations using VISTA data, distinguishing between young and old stars and their motions.

Findings

Detected outward motions indicating galaxy stretching or stripping.

Identified stellar motions related to the Magellanic Bridge and Old Bridge.

Found larger proper motions in young populations within the SMC Wing.

Abstract

We used data from the near-infrared VISTA survey of the Magellanic Cloud system (VMC) to measure proper motions (PMs) of stars within the Small Magellanic Cloud (SMC). The data analysed in this study comprise 26 VMC tiles, covering a total contiguous area on the sky of ~40 deg$^2$. Using multi-epoch observations in the Ks band over time baselines between 13 and 38 months, we calculated absolute PMs with respect to ~130,000 background galaxies. We selected a sample of ~2,160,000 likely SMC member stars to model the centre-of-mass motion of the galaxy. The results found for three different choices of the SMC centre are in good agreement with recent space-based measurements. Using the systemic motion of the SMC, we constructed spatially resolved residual PM maps and analysed for the first time the internal kinematics of the intermediate-age/old and young stellar populations separately. We found outward motions that point either towards a stretching of the galaxy or stripping of its outer regions. Stellar motions towards the North might be related to the "Counter Bridge" behind the SMC. The young populations show larger PMs in the region of the SMC Wing, towards the young Magellanic Bridge. In the older populations, we further detected a coordinated motion of stars away from the SMC in the direction of the Old Bridge as well as a stream towards the SMC.