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23 April 2024

» arxiv » astro-ph/0504035

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Exploring Halo Substructure with Giant Stars VIII: The Velocity Dispersion Profiles of the Ursa Minor and Draco Dwarf Spheroidals At Large Angular Separations
Ricardo R. Munoz ; Peter M. Frinchaboy ; Steven R. Majewski ; Jeffrey R. Kuhn ; Mei-Yin Chou ; Christopher Palma ; Sangmo Tony Sohn ; Richard J. Patterson ; Michael H. Siegel ;
Date:	1 Apr 2005
Journal:	Astrophys.J. 631 (2005) L137-L142
Subject:	astro-ph
Abstract:	We analyze velocity dispersion profiles for the Draco and Ursa Minor (UMi) dwarf spheroidal (dSph) galaxies based on data by Wilkinson et al.(2004) 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 five times more efficiently than simple color-magnitude diagram selection schemes. Previously reported ``cold populations’’ at the R_lim are not obvious in the data and strongly depend on binning: more or less flat and platykurtic dispersion profiles are characteristic of these dSphs at large radii. For either dSph the velocity dispersion of the outermost stars lies within the range of dispersions for stars at other, smaller projected radii. We report discovery of UMi stars to at least 2.7 R_lim (i.e., 210 arcmin or 4 kpc). Even with conservative assumptions, a UMi mass of M> 4.9x10^8 M(sun) is required to bind these stars, implying an unlikely global mass-to-light ratio of M/L>900 (in solar units). We conclude that we have found stars tidally stripped from UMi.
Source:	arXiv, astro-ph/0504035
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