Journal Article

Stellar population constraints on the dark matter content and origin of ultra-compact dwarf galaxies*

Igor V. Chilingarian, Véronique Cayatte and Gilles Bergond

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 390, issue 3, pages 906-912
Published in print November 2008 | ISSN: 0035-8711
Published online October 2008 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.13845.x
Stellar population constraints on the dark matter content and origin of ultra-compact dwarf galaxies*

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We analyse intermediate-resolution Very Large Telescope (VLT) FLAMES/Giraffe spectra of six ultra-compact dwarf (UCD) galaxies in the Fornax cluster. We obtained velocity dispersions and stellar population properties by full spectral fitting against pegase.hr models. Objects span a large range of metallicities (−0.95 to −0.23 dex), four of them are older than 8 Gyr. Comparison of the stellar and dynamical masses suggests that UCDs have little dark matter at best. For one object, UCD3, the Salpeter initial mass function (IMF) results in the stellar mass significantly exceeding the dynamical one, whereas for the Kroupa IMF the values coincide. Although, this object may have peculiar dynamics or/and stellar populations, the Kroupa IMF seems more realistic. We find that UCDs lie well above the metallicity–luminosity relation of early-type galaxies. The same behaviour is demonstrated by some of the massive Milky Way globular clusters, known to contain composite stellar populations. Our results support the two following UCD formation scenario: (i) tidal stripping of nucleated dwarf elliptical galaxies and (ii) formation of tidal superclusters in galaxy mergers. We also discuss some of the alternative channels of the UCD formation binding them to globular clusters.

Keywords: galaxies: dwarf; galaxies: elliptical and lenticular, cD; galaxies: evolution; galaxies: kinematics and dynamics; galaxies: stellar content

Journal Article.  4508 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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