Kinematically Cold Populations at Large Radii in the Draco and Ursa Minor Dwarf Spheroidals

Details Kinematically Cold Populations at Large Radii in the Draco and Ursa Minor Dwarf Spheroidals Kinematically Cold Populations at Large Radii in the Draco and Ursa Minor Dwarf Spheroidals

2004-06-23

arxiv.org/abs/astro-ph/0406520v1

Astrophys.J.611:L21-L24,2004

Astronomy and Astrophysics

Astrophysics

5 pages, accepted for publication in ApJ Letters

Scientific paper

10.1086/423619

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 arcmin (Draco) and ~40 arcmin (UMi). New, deep photometry of Draco reveals a break in the light profile at ~25 arcmin. These data imply the existence of a kinematically cold population in the outer parts of both galaxies. Possible explanations of both the photometric and kinematic data in terms of both equilibrium and non-equilibrium models are discussed in detail. We conclude that these data challenge the picture of dSphs as simple, isolated stellar systems.

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