On Dark Matter in Dwarf Spheroidal Galaxies

¹ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB30HA, UK
² Harvard-Smithsonian Center for Astrophysics, 60 Garden St., MS-51, Cambridge, MA 02138, USA

e-mail: mwalker@cfa.harvard.edu

Abstract

The small (L_V ≤ 10⁷L_V,⊙) baryonic components of the Milky Way’s dwarf spheroidal (dSph) satellites contribute small “backgrounds” with regards to estimates of dSph dark matter density profiles and any related predictions of dark matter decay/annihilation signals. As dSphs gain attention from a broad range of physicists interested in dark matter, it becomes important to examine the robustness – with respect to details like modeling assumptions and observational uncertainties – of conclusions regarding the dark matter content of dSphs and the scaling relations derived therefrom. Indeed dSphs seem to contain copious amounts of dark matter. However, the standard Jeans analysis constrains the dark mass enclosed only within the luminous scale radius, and does not reveal the internal dark matter distribution in a model-indepdendent way. Furthermore, new observational results help to identify complexities in internal dSph kinematics and cast doubt on previously apparent similarities among dSph dark matter halos. Further progress in understsanding dark matter on small scales will require consideration of dSphs more as individual galaxies and less as laboratories.