Issue |
A&A
Volume 448, Number 3, March IV 2006
|
|
---|---|---|
Page(s) | 1031 - 1035 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20054384 | |
Published online | 03 March 2006 |
The transition between star clusters and dwarf galaxies
On the existence of a mass-radius relation for star clusters
of masses >
M
: are these objects formed in
mergers of stellar systems?
1
European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany e-mail: [mkissler;ajordan]@eso.org
2
Astrophysics, Denys Wilkinson Building, University of Oxford, 1 Keble Road, Oxford, OX1 3RH, UK
3
Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK e-mail: bastian@star.ucl.ac.uk
Received:
20
October
2005
Accepted:
24
November
2005
Context.At which masses does the regime of globular clusters end and the one of
dwarf galaxies begin? And what separates these two classes of hot
stellar systems?Aims.We examine to what extend very massive (>) young
star clusters are similar to their lower mass counter parts and to which
degree they resemble other objects in their mass regime
(dwarf-globular transition objects (DGTOs), ultra compact dwarf
galaxies (UCDs), galaxy nuclei).Methods.The comparison is performed by placing the recently observed very massive
young clusters onto known scaling relation defined by globular
clusters (with typical masses
) and/or by hot stellar
systems with sizes up to those of giant galaxies.Results.The very massive (
) young clusters seem to show a
mass-radius relation compatible with the one defined by hot stellar systems
of galaxy mass. This, in turn, can explain their location on the other scaling
relations investigated. It contrasts with the behaviour of the less massive young
clusters and of globular clusters, which do not exhibit any mass-radius
relation. However, the behaviour of the most massive globular clusters is similar to
that of most other objects in that mass regime (
).Conclusions.We show that the properties of the most massive young clusters are compatible with
other objects in the same mass regime such as DGTOs/UCDs. They present a
possible direct avenue of formation for those objects, which does not require
the transformation of a previously existing stellar system.
Simulations and observations support the possibility of the
formation of such very massive young clusters by early mergers of
lower mass stellar clusters, which could explain the emergence of
a mass-radius relation.
© ESO, 2006
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