Abstract
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.
Highlights
The dark matter–dominated Local Group dwarf spheroidal galaxies have emerged as valuable laboratories in which to test dark matter models
In this Letter, we present new observations of the Draco and Ursa Minor (UMi) dwarf spheroidal galaxies (dSph’s) that yield the velocity dispersion profiles of both galaxies to the edge of their light distributions
The new data suggest the existence of kinematically cold populations in the outer parts of both galaxies
Summary
The dark matter–dominated Local Group dwarf spheroidal galaxies (dSph’s) have emerged as valuable laboratories in which to test dark matter models. The projected velocity dispersion profiles of the Fornax and Draco dSph’s have been obtained (Mateo 1997; Kleyna et al 2001). In this Letter, we present new observations of the Draco and Ursa Minor (UMi) dSph’s that yield the velocity dispersion profiles of both galaxies to the edge of their light distributions. The new data suggest the existence of kinematically cold populations in the outer parts of both galaxies. These data make it possible to test the validity of isolated equilibrium models of dSph’s
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
