2004/06/23 by M. I. Wilkinson, J. T. Kleyna, Jan Kleyna +5 · 4 citations
Physics and Astronomy · #Astrophysics and Star Formation Studies #Galaxies: Formation, Evolution, Phenomena #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/423619
published as Astrophys.J.611:L21-L24,2004 · 5 pages, accepted for publication in ApJ Letters
arxiv created 2004/06/23 · openalex publication_date 2004/07/12 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
We present projected velocity dispersion profiles for the Draco and Ursa Minor (UMi) dwarf spheroidal galaxies based on 207 and 162 discrete stellar velocities, respectively. Both profiles show a sharp decline in the velocity dispersion outside ~30' (Draco) and ~40' (UMi). New deep photometry of Draco reveals a break in the light profile at ~25'. These data imply the existence of a kinematically cold population in the outer parts of both galaxies. Possible explanations of both the photometric and the kinematic data in terms of both equilibrium and nonequilibrium models are discussed in detail. We conclude that these data challenge the picture of dwarf spheroidal galaxies as simple, isolated stellar systems.