Internal properties of ultracompact dwarf galaxies in the Virgo cluster

Evstigneeva, E., Gregg, M.D., Drinkwater, M. J. and Hilker, M. (2007) Internal properties of ultracompact dwarf galaxies in the Virgo cluster. The Astronomical Journal, 133 4: 1722-1740. doi:10.1086/511958

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Author Evstigneeva, E.
Gregg, M.D.
Drinkwater, M. J.
Hilker, M.
Title Internal properties of ultracompact dwarf galaxies in the Virgo cluster
Journal name The Astronomical Journal   Check publisher's open access policy
ISSN 0004-6256
Publication date 2007-04
Year available 2007
Sub-type Article (original research)
DOI 10.1086/511958
Open Access Status File (Publisher version)
Volume 133
Issue 4
Start page 1722
End page 1740
Total pages 19
Editor J. S. Gallagher
Place of publication Temple Back, England
Publisher IOP Publishing
Collection year 2008
Language eng
Abstract We present new imaging and spectroscopic observations of six ultracompact dwarf (UCD) galaxies in the Virgo Cluster, along with reanalyzed data for five Fornax Cluster UCDs. These are the most luminous UCDs: -14 mag < M-V < -12 mag. Our Hubble Space Telescope imaging shows that most of the UCDs have shallow or steep cusps in their cores; only one UCD has a flat "King'' core. None of the UCDs show tidal cutoffs down to our limiting surface brightness. Spectroscopic analysis shows that Virgo UCDs are old ( older than 8 Gyr) and have metallicities in the range from [Z/H] = -1.35 to +0.35 dex. Five Virgo UCDs have supersolar [alpha/Fe] abundance ratios, and one Virgo UCD has a solar abundance ratio. The supersolar [alpha/Fe] abundances are typical of old stellar populations found in globular clusters and elliptical galaxies. We find that Virgo UCDs have structural and dynamical properties similar to Fornax UCDs. The Virgo and Fornax UCDs all have masses approximate to(2-9) x 10(7) M-circle dot and mass-to-light ratios approximate to(3-5) M-circle dot/L-circle dot,(V). The dynamical mass-to-light ratios for Virgo UCDs are consistent with simple stellar population model predictions: the Virgo UCDs do not require dark matter to explain their mass-to-light ratios. We conclude that the internal properties of Virgo UCDs are consistent with them being the high-mass/high-luminosity extreme of known globular cluster populations. We refrain from any firm conclusions on Fornax UCD origins until accurate age, metallicity, and alpha-abundance estimates are obtained for them. Some of our results, notably the fundamental plane projections, are consistent with the formation of UCDs by the simple removal of the halo from the nuclei of nucleated dwarf galaxies. However, the ages, metallicities, and abundances for Virgo UCDs are not consistent with this simple stripping model. It might be consistent with more sophisticated models of the stripping process that include the effects of gas removal on the chemical evolution of the nuclei.
Keyword dwarf galaxies
galaxy formation
kinematics and dynamics
Star clusters
Galaxy structure
Hubble Space Telescope
Stellar population synthesis
Infrared Caii Triplet
Massive star clusters
Globular clusters
Fornax cluster
Elliptic galaxies
brightness profiles
Q-Index Code C1

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Created: Thu, 03 Apr 2008, 14:14:21 EST by Jenny Robinson on behalf of School of Mathematics & Physics