Letter to the Editor

The VMC survey^★

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

¹ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
e-mail: fniederhofer@aip.de
² Osservatorio Astronomico di Padova - INAF, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
³ Dipartimento di Fisica e Astronomia, Università di Padova, Vicolo dell’Osservatorio 2, 35122 Padova, Italy
⁴ ICRAR, M468, University of Western Australia, 35 Stirling Hwy, 6009 Crawley, Western Australia, Australia
⁵ Department of Physics and Astronomy, Macquarie University, Balaclava Road, Sydney, NSW 2109, Australia
⁶ International Space Science Institute-Beijing, 1 Nanertiao, Zhongguancun, Hai Dian District, Beijing 100190, PR China
⁷ Astronomy Unit, School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London E1 4NS, UK
⁸ European Southern Observatory, Ave. Alonso de Cordova 3107, Vitacura, Santiago, Chile
⁹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
¹⁰ INAF - Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131, Naples, Italy
¹¹ Lennard-Jones Laboratories, Keele University, ST5 5BG, UK

Received: 2 April 2018
Accepted: 24 April 2018

Abstract

We present the first spatially resolved map of stellar proper motions within the central (~3.1 × 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 ~6.81 deg². 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 approximately 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 (μ_αcos(δ), μ_δ) = (1.087 ± 0.192 (sys.) ± 0.003 (stat.), −1.187 ± 0.008 (sys.) ± 0.003 (stat.)) mas yr⁻¹, consistent with previous studies. Mapping the proper motions as a function of position within the SMC reveals a nonuniform 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.