High mass-to-light ratios of ultra-compact dwarf galaxies - evidence for dark matter?

Baumgardt, H. and Mieske, S. (2008) High mass-to-light ratios of ultra-compact dwarf galaxies - evidence for dark matter?. Monthly Notices of the Royal Astronomical Society, 391 2: 942-948. doi:10.1111/j.1365-2966.2008.13949.x


Author Baumgardt, H.
Mieske, S.
Title High mass-to-light ratios of ultra-compact dwarf galaxies - evidence for dark matter?
Journal name Monthly Notices of the Royal Astronomical Society   Check publisher's open access policy
ISSN 0035-8711
1365-2966
Publication date 2008-12-01
Year available 2008
Sub-type Article (original research)
DOI 10.1111/j.1365-2966.2008.13949.x
Open Access Status DOI
Volume 391
Issue 2
Start page 942
End page 948
Total pages 7
Place of publication Oxford, United Kingdom
Publisher Oxford University Press
Language eng
Abstract Ultra-compact dwarf galaxies (UCDs) are stellar systems with masses of around 107 to 10(8)M(circle dot) and half-mass radii of 10-100 pc. They have some properties in common with massive globular clusters, however dynamical mass estimates have shown that UCDs have mass-to-light ratios which are on average about twice as large than those of globular clusters at comparable metallicity, and tend to be larger than what one would expect for old stellar systems composed out of stars with standard mass functions. One possible explanation for elevated high mass-to-light ratios in UCDs is the existence of a substantial amount of dark matter, which could have ended up in UCDs if they are the remnant nuclei of tidally stripped dwarf galaxies, and dark matter was dragged into these nuclei prior to tidal stripping through, for example, adiabatic gas infall. Tidal stripping of dwarf galaxies has also been suggested as the origin of several massive globular clusters like Omega Cen, in which case one should expect that globular clusters also form with substantial amounts of dark matter in them.
Formatted abstract
Ultra-compact dwarf galaxies (UCDs) are stellar systems with masses of around 107 to 108M and half-mass radii of 10–100 pc. They have some properties in common with massive globular clusters, however dynamical mass estimates have shown that UCDs have mass-to-light ratios which are on average about twice as large than those of globular clusters at comparable metallicity, and tend to be larger than what one would expect for old stellar systems composed out of stars with standard mass functions. One possible explanation for elevated high mass-to-light ratios in UCDs is the existence of a substantial amount of dark matter, which could have ended up in UCDs if they are the remnant nuclei of tidally stripped dwarf galaxies, and dark matter was dragged into these nuclei prior to tidal stripping through, for example, adiabatic gas infall. Tidal stripping of dwarf galaxies has also been suggested as the origin of several massive globular clusters like Omega Cen, in which case one should expect that globular clusters also form with substantial amounts of dark matter in them. In this paper, we present collisional N-body simulations which study the co-evolution of
a system composed out of stars and dark matter. We find that the dark matter gets removed from the central regions of such systems due to dynamical friction and mass segregation of stars. The friction time-scale is significantly shorter than a Hubble time for typical globular clusters, while most UCDs have friction times much longer than a Hubble time. Therefore, a significant dark matter fraction remains within the half-mass radius of present-day UCDs, making dark matter a viable explanation for the elevated M/L ratios of UCDs. If at least some globular clusters formed in a way similar to UCDs, we predict a substantial amount of dark matter in their outer parts.
Keyword Stellar dynamics
Methods: N-body simulations
Galaxies: star clusters
Globular-Clusters
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Non-UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Mathematics and Physics
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