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Compact Stellar Systems in the Fornax Cluster: Super-massive Star Clusters or Extremely Compact Dwarf Galaxies?

Published online by Cambridge University Press:  05 March 2013

M. J. Drinkwater ,
J. B. Jones ,
M. D. Gregg  and
S. Phillipps
M. J. Drinkwater
Affiliation:
School of Physics, University of Melbourne, Vic. 3010, Australia; m.drinkwater@physics.unimelb.edu.au
J. B. Jones
Affiliation:
Department of Physics, University of Bristol, Tyndall Avenue, Bristol, BS8 1TL, UK; B.Jones@bristol.ac.uk
M. D. Gregg
Affiliation:
University of California, Davis, and Institute for Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, L-413, Livermore, CA 94550, USA; gregg@igpp.ucllnl.org
S. Phillipps
Affiliation:
Department of Physics, University of Bristol, Tyndall Avenue, Bristol, BS8 1TL, UK; S.Phillipps@bristol.ac.uk
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Abstract

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We describe a population of compact objects in the centre of the Fornax Cluster which were discovered as part of our 2dF Fornax Spectroscopic Survey. These objects have spectra typical of old stellar systems, but are unresolved on photographic sky survey plates. They have absolute magnitudes −13 < MB < −11, so they are 10 times more luminous than any Galactic globular clusters, but fainter than any known compact dwarf galaxies. These objects are all within 30 arcminutes of the central galaxy of the cluster, NGC 1399, but are distributed over larger radii than the globular cluster system of that galaxy. We suggest that these objects are either super-massive star clusters (intra-cluster globular clusters or tidally stripped nuclei of dwarf galaxies) or a new type of low-luminosity, compact elliptical dwarf (‘M32-type”) galaxy. The best way to test these hypotheses will be to obtain high-resolution imaging and high-dispersion spectroscopy to determine their structures and mass-to-light ratios. This will allow us to compare them to known compact objects and establish whether they represent a new class of hitherto unknown stellar system.

Keywords

galaxies: star clustersgalaxies: dwarfgalaxies: formation

Information

Type
Research Article
Information
Publications of the Astronomical Society of Australia , Volume 17 , Issue 3 , 2000 , pp. 227 - 233
Copyright
Copyright © Astronomical Society of Australia 2000

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