The VMC survey XXX. Stellar proper motions in the central parts of the Small Magellanic Cloud

TL;DR

This study provides the first detailed map of stellar proper motions in the central region of the Small Magellanic Cloud, revealing complex velocity patterns and tidal features using near-infrared data from the VISTA survey.

Contribution

It presents a spatially resolved proper motion map of the SMC's central area, calibrated with background galaxies, and identifies non-uniform velocity patterns indicating tidal interactions.

Findings

Detected a non-uniform velocity pattern across the SMC

Identified a tidal feature behind the main body of the SMC

Observed a star flow in the South-East along the line-of-sight

Abstract

We present the first spatially resolved map of stellar proper motions within the central ($\sim$3.1 $\times$ 2.4 kpc) regions of the Small Magellanic Cloud (SMC). The data used for this study encompasses four tiles from the ongoing near-infrared VISTA survey of the Magellanic Clouds system and covers a total contiguous area on the sky of $\sim$6.81 deg$^2$. Proper motions have been calculated independently in two dimensions from the spatial offsets in the $K_s$ filter over time baselines between 22 and 27 months. The reflex motions of $\sim$33~000 background galaxies are used to calibrate the stellar motions to an absolute scale. The resulting catalog is composed of more than 690 000 stars which have been selected based on their position in the $(J-K_s, K_s)$ color-magnitude diagram. For the median absolute proper motion of the SMC, we find ($\mu_{\alpha}\mathrm{cos}(\delta)$, $\mu_{\delta}$) = (1.087 $\pm$ 0.192 (sys.) $\pm$ 0.003 (stat.), $-$1.187 $\pm$ 0.008 (sys.) $\pm$ 0.003 (stat.)) mas yr$^{-1}$, consistent with previous studies. Mapping the proper motions as a function of position within the SMC reveals a non uniform velocity pattern indicative of a tidal feature behind the main body of the SMC and a flow of stars in the South-East moving predominantly along the line-of-sight.