First Clear Signature of an Extended Dark Matter Halo in the Draco Dwarf Spheroidal

Details First Clear Signature of an Extended Dark Matter Halo in the Draco Dwarf Spheroidal First Clear Signature of an Extended Dark Matter Halo in the Draco Dwarf Spheroidal

Publishing date

2001-11-16

URL

arxiv.org/abs/astro-ph/0111329v1

Science

Astronomy and Astrophysics

Field

Astrophysics

Additional info

to be published in ApJL; 5 pages, 4 figures

Type

Scientific paper

Digital Object Identifier

10.1086/338603

Abstract

We present the first clear evidence for an extended dark matter halo in the Draco dwarf spheroidal galaxy based on a sample of new radial velocities for 159 giant stars out to large projected radii. Using a two parameter family of halo models spanning a range of density profiles and velocity anisotropies, we are able to rule out (at about the 2.5 sigma confidence level) haloes in which mass follows light. The data strongly favor models in which the dark matter is significantly more extended than the visible dwarf. However, haloes with harmonic cores larger than the light distribution are also excluded. When combined with existing measurements of the proper motion of Draco, our data strongly suggest that Draco has not been tidally truncated within ~1 kpc. We also show that the rising velocity dispersion at large radii represents a serious problem for modified gravity (MOND).

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