Matthew G. Walker, Mario Mateo, Edward W. Olszewski, Sergey Koposov, Vasily Belokurov, Prashin Jethwa, David L. Nidever, Vincent Bonnivard, John I.Bailey Iii, Eric F. Bell, Sarah R. Loebman

Research output: Contribution to journalArticlepeer-review

102 Scopus citations


We present results from spectroscopic observations with the Michigan/Magellan Fiber System (M2FS) of 147 stellar targets along the line of sight to the newly discovered "ultrafaint" stellar systems Tucana 2 (Tuc 2) and Grus 1 (Gru 1). Based on simultaneous estimates of line of sight velocity and stellar-atmospheric parameters, we identify 8 and 7 stars as probable members of Tuc 2 and and Gru 1, respectively. Our sample for Tuc 2 is sufficient to resolve an internal velocity dispersion of km s-1 about a mean of km s-1 (solar rest frame), and to estimate a mean metallicity of [Fe/H] =. These results place Tuc 2 on chemodynamical scaling relations followed by dwarf galaxies, suggesting a dominant dark matter component with dynamical mass enclosed within the central ∼160 pc, and dynamical mass-to-light ratio . For Gru 1 we estimate a mean velocity of km s-1 and a mean metallicity of [Fe/H] = but our sample does not resolve Gru 1's velocity dispersion. The radial coordinates of Tuc 2 and Gru 1 in Galactic phase space suggest that their orbits are among the most energetic within a distance of . Moreover, their proximity to each other in this space arises naturally if both objects are trailing the Large Magellanic Cloud.

Original languageEnglish (US)
Article number53
JournalAstrophysical Journal
Issue number1
StatePublished - Mar 1 2016


  • Local Group
  • galaxies: dwarf
  • galaxies: individual (Tucana 2, Gru 1)
  • galaxies: kinematics and dynamics
  • techniques: spectroscopic

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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