Arxiv:1806.02345V2 [Astro-Ph.GA] 18 Feb 2019
Draft version February 20, 2019 Preprint typeset using LATEX style emulateapj v. 12/16/11 PROPER MOTIONS OF MILKY WAY ULTRA-FAINT SATELLITES WITH Gaia DR2 × DES DR1 Andrew B. Pace1,4 and Ting S. Li2,3 1 George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, and Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843, USA 2 Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510, USA and 3 Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637, USA Draft version February 20, 2019 ABSTRACT We present a new, probabilistic method for determining the systemic proper motions of Milky Way (MW) ultra-faint satellites in the Dark Energy Survey (DES). We utilize the superb photometry from the first public data release (DR1) of DES to select candidate members, and cross-match them with the proper motions from Gaia DR2. We model the candidate members with a mixture model (satellite and MW) in spatial and proper motion space. This method does not require prior knowledge of satellite membership, and can successfully determine the tangential motion of thirteen DES satellites. With our method we present measurements of the following satellites: Columba I, Eridanus III, Grus II, Phoenix II, Pictor I, Reticulum III, and Tucana IV; this is the first systemic proper motion measurement for several and the majority lack extensive spectroscopic follow-up studies. We compare these to the predictions of Large Magellanic Cloud satellites and to the vast polar structure. With the high precision DES photometry we conclude that most of the newly identified member stars are very metal-poor ([Fe/H] .
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