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Title:
Leo V: Spectroscopy of a Distant and Disturbed Satellite
Authors:
Walker, M. G.; Belokurov, V.; Evans, N. W.; Irwin, M. J.; Mateo, M.; Olszewski, E. W.; Gilmore, G.
Affiliation:
AA(Institute of Astronomy, University of Cambridge, UK ), AB(Institute of Astronomy, University of Cambridge, UK ), AC(Institute of Astronomy, University of Cambridge, UK ), AD(Institute of Astronomy, University of Cambridge, UK ), AE(Department of Astronomy, University of Michigan, Ann Arbor, MI, USA ), AF(Steward Observatory, The University of Arizona, Tucson, AZ, USA), AG(Institute of Astronomy, University of Cambridge, UK )
Publication:
The Astrophysical Journal Letters, Volume 694, Issue 2, pp. L144-L147 (2009). (ApJL Homepage)
Publication Date:
04/2009
Origin:
IOP
ApJ Keywords:
dark matter, galaxies: dwarf, galaxies: kinematics and dynamics, Local Group
DOI:
10.1088/0004-637X/694/2/L144
Bibliographic Code:
2009ApJ...694L.144W

Abstract

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') and have a velocity dispersion of 2.4+2.4 -1.4 km s-1. The other two likely members lie near each other but far from the center (R ~ 13' ~ 700 pc) and inflate the global velocity dispersion to 3.7+2.3 -1.4 km s-1. Assuming the five central members are bound, we obtain a dynamical mass of M = 3.3+9.1 -2.5 × 105 M sun (M/LV = 75+230 -58[M/LV ]sun). From the stacked spectrum of the five central members we estimate a mean metallicity of [Fe/H]=-2.0 ± 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.

Observations reported here were obtained at the MMT Observatory, a facility operated jointly by the University of Arizona and the Smithsonian Institution.

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