{
  "id": "1805.01448",
  "version": "v1",
  "published": "2018-05-03T17:47:43.000Z",
  "updated": "2018-05-03T17:47:43.000Z",
  "title": "The Missing Satellites of the Magellanic Clouds? Gaia Proper Motions of the Recently Discovered Ultra-Faint Galaxies",
  "authors": [
    "Nitya Kallivayalil",
    "Laura Sales",
    "Paul Zivick",
    "Tobias K. Fritz",
    "Andrés Del Pino",
    "Sangmo Tony Sohn",
    "Gurtina Besla",
    "Roeland P. van der Marel",
    "Julio F. Navarro",
    "Elena Sacchi"
  ],
  "comment": "10 pages, 7 figures, 3 tables. Submitted to AAS Journals",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "According to LCDM theory, hierarchical evolution should occur on all mass scales, implying that satellites of the Milky Way also once had companions. The recent discovery of several ultra-faint dwarf galaxy candidates in close proximity to the Magellanic Clouds provides a unique opportunity to test this theory. Specifically, proper motions provide a stringent test, because material that is associated with the Large Magellanic Cloud prior to infall should retain its direction of orbital angular momentum. We present proper motion measurements for 13 of the 32 newly discovered dwarf galaxy candidates using Gaia data release 2. All 13 also have radial velocity measurements. We compare the measured 3D velocities of these dwarfs to those expected at the corresponding distance and location for the debris of an LMC analog in a numerical simulation. We conclude that 4 of these galaxies (Hor1, Car2, Car3 and Hyd1) have come in with the Magellanic Cloud system, constituting the first confirmation of the type of satellite infall predicted by LCDM. Ret2, Tuc2 and Gru1 have some velocity components that are not consistent within 3 sigma of our predictions and are therefore less favorable. Hyd2 and Dra2 could be associated with the LMC and merit further attention. We rule out Tuc3, Cra2, Tri2 and Aqu2 as potential members. Of the dwarfs without measured PMs, 6 of them are deemed unlikely on the basis of their positions and distances alone which put them too far from the orbital plane expected for LMC debris (Eri2, Ind2, Cet2, Tri2, Cet3 and Vir1). For the remaining sample, we use the simulation to predict proper motions and radial velocities, finding that Phx2 has an overdensity of stars in DR2 consistent with this PM prediction. If its radial velocity is confirmed at $\\sim -15$ km s$^{-1}, it is also likely a member.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2018-05-03T17:47:43.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "gaia proper motions",
      "ultra-faint galaxies",
      "missing satellites",
      "radial velocity",
      "large magellanic cloud prior"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 10,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}