Abstract
We present results from spectroscopic observations with the Michigan/Magellan Fiber System (M2FS) of 182 stellar targets along the line of sight (LOS) to the newly discovered "ultrafaint" object Reticulum 2 (Ret 2). For 37 of these targets, the spectra are sufficient to provide simultaneous estimates of LOS velocity (, median random error km s−1), effective temperature (, K), surface gravity (, dex), and iron abundance (, dex). We use these results to confirm 17 stars as members of Ret 2. From the member sample we estimate a velocity dispersion of km s−1 about a mean of km s−1 in the solar rest frame ( km s−1 in the Galactic rest frame), and a metallicity dispersion of dex about a mean of . These estimates marginalize over possible velocity and metallicity gradients, which are consistent with zero. Our results place Ret 2 on chemodynamical scaling relations followed by the Milky Way's dwarf-galactic satellites. Under assumptions of dynamic equilibrium and negligible contamination from binary stars—both of which must be checked with deeper imaging and repeat spectroscopic observations—the estimated velocity dispersion suggests a dynamical mass of enclosed within projected halflight radius pc, with mass-to-light ratio in solar units.
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