The Orbital Histories of Magellanic Satellites Using Gaia DR2 Proper Motions

Ekta Patel, Nitya Kallivayalil, Nicolas Garavito-Camargo, Gurtina Besla, Daniel R. Weisz, Roeland P. van der Marel, Michael Boylan-Kolchin, Marcel S. Pawlowski, Facundo A. Gómez

Published 2020-01-06Version 1

With the release of Gaia DR2, it is now possible to measure the proper motions (PMs) of the lowest mass, ultra-faint satellites in the Milky Way's (MW) halo for the first time. Many of these faint satellites are posited to have been accreted as satellites of the Magellanic Clouds (MCs). Using their 6D phase space information, we calculate the orbital histories of 13 ultra-faint satellites and five classical satellites in a combined MW+LMC+SMC potential to determine which galaxies are dynamically associated with the LMC/SMC. We identify three classes of galaxies that have recently interacted with the MCs: i.) MW satellites on high-speed orbits that made a close approach ($< 100$ kpc) to the MCs $< 1$ Gyr ago (Sculptor 1, Tucana 3, Segue 1); ii.) short-term Magellanic satellites that have completed one recent, close pericentric passage (Reticulum 2, Phoenix 2); and iii.) long-term Magellanic satellites that have completed two consecutive recent, close passages (Carina 2, Carina 3, Horologium 1, Hydrus 1). Results are reported for a range of MW and LMC masses. Contrary to previous work, we find no dynamical association between Carina, Fornax, and the MCs. We find that Aquarius 2, Canes Venatici 2, Crater 2, Draco 1, Draco 2, Hydra 2, and Ursa Minor are not members of the Magellanic system. Finally, we determine that the addition of the SMC's gravitational potential affects the longevity of satellites as members of the Magellanic system (short-term versus long-term satellites), but it does not change the total population of Magellanic satellites.