Magellan/M2FS Spectroscopy of Tucana 2 and Grus 1

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

Research output: Contribution to journalArticlepeer-review

Abstract

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 8.6+4.4−2.7 km s−1 about a mean of −129.1+3.5−3.5 km s−1 (solar rest frame), and to estimate a mean metallicity of [Fe/H]= −2.23+0.18−0.12. These results place Tuc 2 on chemodynamical scaling relations followed by dwarf galaxies, suggesting a dominant dark matter component with dynamical mass 2.7+3.1−1.3×106 M⊙ enclosed within the central ∼160 pc, and dynamical mass-to-light ratio 1900+2200−900 M⊙/LV,⊙. For Gru 1 we estimate a mean velocity of −140.5+2.4−1.6 km s−1 and a mean metallicity of [Fe/H]=−1.42+0.55−0.42, 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 distance ≤300 kpc. Moreover, their proximity to each other in this space arises naturally if both objects are trailing the Large Magellanic Cloud.
Original languageEnglish
JournalAstrophysical Journal
DOIs
Publication statusPublished - 26 Feb 2016

Keywords

  • astro-ph.GA

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