A Dynamical Fossil in the Ursa Minor Dwarf Spheroidal Galaxy

Astrophysics, abstract
astro-ph/0304093

From: N.W. Evans <w.evans1@physics.oxford.ac.uk>

Date: Fri, 4 Apr 2003 16:13:25 GMT   (46kb)

Authors:
Jan T. Kleyna (Cambridge),
Mark I. Wilkinson (Cambridge),
Gerard Gilmore (Cambridge),
N. Wyn Evans (Cambridge)

Comments: Astrophysical Journal (Letters), in press

The nearby Ursa Minor dwarf spheroidal (UMi dSph) is one of the most dark
matter dominated galaxies known, with a central mass to light ratio roughly
equal to 70. Somewhat anomalously, it appears to contain morphological
substructure in the form of a second peak in the stellar number density. It is
often argued that this substructure must be transient because it could not
survive for the > 10 Gyr age of the system, given the crossing time implied by
UMi’s 8.8 km/s internal velocity dispersion. In this paper, however, we present
evidence that the substructure has a cold kinematical signature, and argue that
UMi’s clumpiness could indeed be a primordial artefact. Using numerical
simulations, we demonstrate that substructure is incompatible with the cusped
dark matter haloes predicted by the prevailing Cold Dark Matter (CDM) paradigm,
but is consistent with an unbound stellar cluster sloshing back and forth
within the nearly harmonic potential of a cored dark matter halo. Thus CDM
appears to disagree with observation at the least massive, most dark matter
dominated end of the galaxy mass spectrum.

References and citations for this submission:

SLAC-SPIRES HEP (refers to ,
cited by, arXiv reformatted)