The chemical composition of ultracompact dwarf galaxies in the Virgo and Fornax clusters

Francis, K. J., Drinkwater, M. J., Chilingarian, Igor V., Bolt, A. M. and Firth, P. (2012) The chemical composition of ultracompact dwarf galaxies in the Virgo and Fornax clusters. Monthly Notices of the Royal Astronomical Society, 425 1: 325-337. doi:10.1111/j.1365-2966.2012.21465.x


Author Francis, K. J.
Drinkwater, M. J.
Chilingarian, Igor V.
Bolt, A. M.
Firth, P.
Title The chemical composition of ultracompact dwarf galaxies in the Virgo and Fornax clusters
Journal name Monthly Notices of the Royal Astronomical Society   Check publisher's open access policy
ISSN 0035-8711
1365-2966
Publication date 2012-09
Sub-type Article (original research)
DOI 10.1111/j.1365-2966.2012.21465.x
Open Access Status DOI
Volume 425
Issue 1
Start page 325
End page 337
Total pages 13
Place of publication Oxford, United Kingdom
Publisher Oxford University Press
Collection year 2013
Language eng
Formatted abstract
We present spectroscopic observations of ultracompact dwarf (UCD) galaxies in the Fornax and Virgo clusters made to measure and compare their stellar populations. The spectra were obtained on the Gemini-North (Virgo) and Gemini-South (Fornax) telescopes using the respective Gemini Multi-Object Spectrographs. We estimated the ages, metallicities and abundances of the objects from measurements of Lick line-strength indices in the spectra; we also estimated the ages and metallicities independently using a direct spectral fitting technique. Both methods revealed that the UCDs are old (mean age 10.8 ± 0.7 Gyr) and (generally) metal rich (mean [Fe/H] = -0.8 ± 0.1). The α-element abundances of the objects measured from the Lick indices are super-solar. We used these measurements to test the hypothesis that UCDs are formed by the tidal disruption of present-day nucleated dwarf elliptical galaxies. The data are not consistent with this hypothesis because both the ages and abundances are significantly higher than those of observed dwarf galaxy nuclei (this does not exclude disruption of an earlier generation of dwarf galaxies). They are more consistent with the properties of globular star clusters, although at higher mean metallicity. The UCDs display a very wide range of metallicity (-1.7 < [Fe/H] < 0.0), spanning the full range of both globular clusters and dwarf galaxy nuclei. We confirm previous reports that most UCDs have high metalliticities for their luminosities, lying significantly above the canonical metallicitiy-luminosity relation followed by early-type galaxies. In contrast to previous work, we find that there is no significant difference in either the mean ages or the mean metallicities of the Virgo and Fornax UCD populations.
Keyword Galaxies: dwarf
Galaxies: formation
Galaxies: star clusters: general
Galaxies: stellar content
Compact Stellar-Systems
Element Abundance Ratios
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Mathematics and Physics
Official 2013 Collection
 
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