Evidence for two populations of Galactic globular clusters from the ratio of their half-mass to Jacobi radii

Baumgardt, H, Parmentier, G, Gieles, M and Vesperini, E (2010) Evidence for two populations of Galactic globular clusters from the ratio of their half-mass to Jacobi radii. Monthly Notices of the Royal Astronomical Society, 401 3: 1832-1838. doi:10.1111/j.1365-2966.2009.15758.x


Author Baumgardt, H
Parmentier, G
Gieles, M
Vesperini, E
Title Evidence for two populations of Galactic globular clusters from the ratio of their half-mass to Jacobi radii
Journal name Monthly Notices of the Royal Astronomical Society   Check publisher's open access policy
ISSN 0035-8711
1365-2966
Publication date 2010-01-01
Year available 2009
Sub-type Article (original research)
DOI 10.1111/j.1365-2966.2009.15758.x
Open Access Status DOI
Volume 401
Issue 3
Start page 1832
End page 1838
Total pages 7
Place of publication Oxford, United Kingdom
Publisher Oxford University Press
Language eng
Abstract We investigate the ratio between the half-mass radii r(h) of Galactic globular clusters and their Jacobi radii r(J) given by the potential of the Milky Way and show that clusters with galactocentric distances R(GC) > 8 kpc fall into two distinct groups: one group of compact, tidally underfilling clusterswith r(h)/r(J) < 0.05 and another group of tidally filling clusters which have 0.1 < r(h)/r(J) < 0.3. We find no correlation between the membership of a particular cluster in one of these groups and its membership in the old or younger halo population. Based on the relaxation times and orbits of the clusters, we argue that compact clusters and most clusters in the inner Milky Way were born compact with half-mass radii r(h) < 1 pc. Some of the tidally filling clusters might have formed compact as well, but the majority likely formed with large half-mass radii. Galactic globular clusters therefore show a similar dichotomy as was recently found for globular clusters in dwarf galaxies and for young star clusters in the Milky Way. It seems likely that some of the tidally filling clusters are evolving along the main-sequence line of clusters recently discovered by Kupper et al. (2008) and are in the process of dissolution.
Formatted abstract
We investigate the ratio between the half-mass radii rh of Galactic globular clusters and their Jacobi radii rJ given by the potential of the Milky Way and show that clusters with galactocentric distances RGC > 8 kpc fall into two distinct groups: one group of compact, tidally underfilling clusters with rh/rJ < 0.05 and another group of tidally filling clusters which have 0.1 < rh/rJ < 0.3. We find no correlation between the membership of a particular cluster in one of these groups and its membership in the old or younger halo population. Based on the relaxation times and orbits of the clusters, we argue that compact clusters and most clusters in the inner Milky Way were born compact with half-mass radii r h < 1 pc. Some of the tidally filling clusters might have formed compact as well, but the majority likely formed with large half-mass radii. Galactic globular clusters therefore show a similar dichotomy as was recently found for globular clusters in dwarf galaxies and for young star clusters in the Milky Way. It seems likely that some of the tidally filling clusters are evolving along the main-sequence line of clusters recently discovered by Küpper et al. (2008) and are in the process of dissolution.
Copyright © 1999–2011 John Wiley & Sons, Inc. All Rights Reserved.
Keyword Globular clusters
General
Q-Index Code CX
Q-Index Status Confirmed Code
Grant ID NNX08AH15G
PHY05-51164
Institutional Status Non-UQ
Additional Notes First published online: 12 Nov 2009

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Mathematics and Physics
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Created: Wed, 23 Feb 2011, 01:08:36 EST by Dr Holger Baumgardt on behalf of Physics