Leo V: Spectroscopy of a Distant and Disturbed Satellite
  We present a spectroscopic study of Leo V, a recently discovered satellite of
the Milky Way (MW). From stellar spectra obtained with the MMT/Hectochelle
spectrograph we identify seven likely members of Leo V. Five cluster near the
Leo V center (R < 3 arcmin) and have velocity dispersion 2.4_{-1.4}^{+2.4}
km/s. The other two likely members lie near each other but far from the center
(R~13 arcmin ~ 700 pc) and inflate the global velocity dispersion to
3.7_{-1.4}^{+2.3} km/s. Assuming the five central members are bound, we obtain
a dynamical mass of M=3.3_{-2.5}^{+9.1} x 10^5M_{sun}
(M/L_V=75_{-58}^{+230}[M/L_V]_{sun}). From the stacked spectrum of the five
central members we estimate a mean metallicity of [Fe/H]=-2.0\pm 0.2 dex. Thus
with respect to dwarf spheroidals of similar luminosity, Leo V is slightly less
massive and slightly more metal-rich. Since we resolve the central velocity
dispersion only marginally, we do not rule out the possibility that Leo V is a
diffuse star cluster devoid of dark matter. The wide separation of its two
outer members implies Leo V is losing mass; however, its large distance (D ~
180 kpc) is difficult to reconcile with MW tidal stripping unless the orbit is
very radial.
