The Missing Satellites of the Magellanic Clouds? Gaia Proper Motions of the Recently Discovered Ultra-faint Galaxies

Nitya Kallivayalil, Laura V. Sales, Paul Zivick, Tobias K. Fritz, Andrés Del Pino, Sangmo Tony Sohn, Gurtina Besla, Roeland P. Van Der Marel, Julio F. Navarro, Elena Sacchi

Research output: Contribution to journalArticlepeer-review

108 Scopus citations


According to LCDM theory, hierarchical evolution occurs on all mass scales, implying that satellites of the Milky Way should also have companions. The recent discovery of ultra-faint dwarf galaxy candidates in close proximity to the Magellanic Clouds provides an opportunity to test this theory. We present proper motion (PM) measurements for 13 of the 32 new 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 a Large Magellanic Cloud (LMC) analog in a cosmological numerical simulation. We conclude that four of these galaxies (Hor1, Car2, Car3, and Hyi1) have come in with the Magellanic Clouds, constituting the first confirmation of the type of satellite infall predicted by LCDM. Ret2, Tuc2, and Gru1 have velocity components that are not consistent within 3σ of our predictions and are therefore less favorable. Hya2 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, five of them are deemed unlikely on the basis of their positions and distances alone being too far from the orbital plane expected for LMC debris (Eri2, Ind2, Cet2, Cet3, and Vir1). For the remaining sample, we use the simulation to predict PMs and radial velocities, finding that Phx2 has an overdensity of stars in DR2 consistent with this PM prediction.

Original languageEnglish (US)
Article number19
JournalAstrophysical Journal
Issue number1
StatePublished - Nov 1 2018


  • Local Group
  • Magellanic Clouds
  • dark matter
  • galaxies: interactions
  • galaxies: kinematics and dynamics
  • proper motions

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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