Astrophys. J., 808, 108 (2015/August-1)
Magellan/M2FS spectroscopy of the Reticulum 2 dwarf spheroidal galaxy.
WALKER M.G., MATEO M., OLSZEWSKI E.W., BAILEY III J.I., KOPOSOV S.E., BELOKUROV V. and EVANS N.W.
Abstract (from CDS):
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 (νilos, median random error δνlos = 1.4 km/s), effective temperature (Teff, δTef = 478 K), surface gravity (log g, δ_log g_ = 0.63 dex), and iron abundance ([Fe/H], δ[Fe/H] = 0.47 dex). We use these results to confirm 17 stars as members of Ret 2. From the member sample we estimate a velocity dispersion of σνlos = 3.6–0.7+1.0 km/s about a mean of <νlos> = 64.31.2+1.2 km/s in the solar rest frame (~-90.9 km/s in the Galactic rest frame), and a metallicity dispersion of σ[Fe/H] = 0.49–0.14+0.19 dex about a mean of <[Fe/H]_> = -2.58–0.33+0.34. 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 M(Rh)≈5Rhσνlos2/(2G) = 2.4–0.8+1.4 x 105M☉ enclosed within projected halflight radius Rh ∼ 32 pc pc, with mass-to-light ratio ≈ 2M(Rh)/LV = 467–168+286 in solar units.
galaxies: dwarf - galaxies: individual: Reticulum 2 - galaxies: kinematics and dynamics - Local Group - methods: data analysis - techniques: spectroscopic
VizieR on-line data:
<Available at CDS (J/ApJ/808/108): table1.dat>
Table 1: [WMO2015] NNN N=38 among (Nos 4-178).
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