Structural properties of ultra-compact dwarf galaxies in the Fornax and Virgo Clusters

Evstigneeva, E. A., Drinkwater, M. J., Peng, C. Y., Hilker, M., De Propris, R., Jones, J. B., Phillipps, S., Gregg, M. D. and Karick, A. M. (2008) Structural properties of ultra-compact dwarf galaxies in the Fornax and Virgo Clusters. The Astronomical Journal, 136 1: 461-478. doi:10.1088/0004-6256/136/1/461

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Author Evstigneeva, E. A.
Drinkwater, M. J.
Peng, C. Y.
Hilker, M.
De Propris, R.
Jones, J. B.
Phillipps, S.
Gregg, M. D.
Karick, A. M.
Title Structural properties of ultra-compact dwarf galaxies in the Fornax and Virgo Clusters
Journal name The Astronomical Journal   Check publisher's open access policy
ISSN 0004-6256
2330-9458
Publication date 2008-07
Sub-type Article (original research)
DOI 10.1088/0004-6256/136/1/461
Open Access Status File (Publisher version)
Volume 136
Issue 1
Start page 461
End page 478
Total pages 18
Editor J. S. Gallagher III
Place of publication Washington, DC 20009 United States
Publisher American Astronomical Society
Collection year 2009
Language eng
Abstract We present a detailed analysis of high-resolution two-band Hubble Space Telescope Advanced Camera for Surveys imaging of 21 ultra-compact dwarf (UCD) galaxies in the Virgo and Fornax Clusters. The aim of this work is to test two formation hypotheses for UCDs—whether they are bright globular clusters (GCs) or stripped ("threshed") early-type dwarf galaxies—by direct comparison of UCD structural parameters and colors with GCs and galaxy nuclei. We find that the UCD surface brightness profiles can be described by a range of models and that the luminous UCDs in particular cannot be described by standard King models with tidal cutoffs as they have extended outer halos. This is not expected from traditional King models of GCs, but is consistent with recent results for massive GCs. The total luminosities, colors, and sizes of the UCDs (their position in the color-magnitude and luminosity-size diagrams) are consistent with them being either luminous GCs or threshed nuclei of both early-type and late-type galaxies (not just early-type dwarfs). For the most luminous UCDs we estimate color gradients over a limited range of radius. These are systematically positive in the sense of getting redder outward: mean Δ(F606W – F814W) = 0.14 mag per 100 pc with rms = 0.06 mag per 100 pc. The positive gradients found in the bright UCDs are consistent with them being either bright GCs or threshed early-type dwarf galaxies (except VUCD3). In contrast to the above results we find a very significant (>99.9% significance) difference in the sizes of UCDs and early-type galaxy nuclei: the effective radii of UCDs are 2.2+0.2 –0.1 times larger than those of early-type galaxy nuclei at the same luminosity. This result suggests that an important test can be made of the threshing hypothesis by simulating the process and predicting what size increase is expected.
Keyword galaxies : clusters : individual (Fornax Cluster, Virgo Cluster)
galaxies: dwarf
galaxies: formation
galaxies: fundamental parameters
galaxies: star clusters
galaxies: structure
Q-Index Code C1
Q-Index Status Confirmed Code
Additional Notes Published online 2008 June 13

Document type: Journal Article
Sub-type: Article (original research)
Collections: 2009 Higher Education Research Data Collection
School of Mathematics and Physics
 
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Created: Wed, 25 Mar 2009, 12:45:56 EST by Jo Hughes on behalf of School of Mathematics & Physics