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.
- 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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Walker, M. G. (Creator), Mateo, M. (Creator), Olszewski, E. W. (Creator), Koposov, S. (Creator), Belokurov, V. (Creator), Jethwa, P. (Creator), Nidever, D. L. (Creator), Bonnivard, V. (Creator), Iii, J. I. B. (Contributor), Bell, E. F. (Creator), Loebman, S. R. (Creator) & Bailey III, J. I. (Contributor), Centre de Donnees Strasbourg (CDS), 2016