Journal
ASTROPHYSICAL JOURNAL
Volume 631, Issue 2, Pages L137-L141Publisher
IOP PUBLISHING LTD
DOI: 10.1086/497396
Keywords
galaxies : individual ( Draco dwarf spheroidal, Ursa Minor dwarf spheroidal); galaxies : kinematics and dynamics; Local Group
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We analyze velocity dispersion profiles for the Draco and Ursa Minor (UMi) dwarf spheroidal (dSph) galaxies based on published and new Keck HIRES spectra for stars in the outer UMi field. Washington + DDO51 filter photometric catalogs provide additional leverage on membership of individual stars and, beyond 0.5 King limiting radii (r(lim)), identify bona fide dSph members up to 4.5 times more efficiently than simple color-magnitude diagram selections. Previously reported cold populations at r(lim) are not obvious in the data and appear only with particular binning; more or less constant and platykurtic dispersion profiles are characteristic of these dSphs to large radii. We report the discovery of UMi stars to at least 2.7r(lim) (i.e., 210' or 4 kpc). Even with conservative assumptions, a UMi mass of M > 4.9 x 10(8) M-circle dot is required to bind these stars, implying an unlikely global mass-to-light ratio M/L > 900 (M/L)(circle dot). We conclude that we have found stars tidally stripped from UMi.
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