Volume 565, May 2014
|Number of page(s)||16|
|Published online||16 May 2014|
Chemical composition and constraints on mass loss for globular clusters in dwarf galaxies: WLM and IKN ⋆,⋆⋆
Department of Astrophysics/IMAPPRadboud University Nijmegen,
PO Box 9010,
2 UCO/Lick Observatory, University of California, Santa Cruz CA 95064, USA
3 Centre for Astrophysics & Supercomputing, Swinburne University of Technology, VIC 3122 Hawthorn, Australia
4 Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA
Received: 14 September 2013
Accepted: 5 April 2014
Aims. We determine the metallicities of globular clusters (GCs) in the WLM and IKN dwarf galaxies, using VLT/UVES and Keck/ESI spectroscopy. These measurements are combined with literature data for field stars to constrain GC formation scenarios. For the WLM GC, we also measure detailed abundance ratios for a number of light, α, Fe-peak, and n-capture elements, which are compared with literature data for the Fornax dSph and the Milky Way.
Methods. The abundances are derived by computing synthetic integrated-light model spectra and adjusting the input composition until the best fits to the observed spectra are obtained.
Results. We find low metallicities of [Fe/H] = −2.0 and −2.1 for the WLM GC and the GC IKN-5, respectively. We estimate that 17%–31% of the stars with [Fe/H] ≤ −2 in WLM belong to the GC, and IKN-5 may even contain a similar number of metal-poor stars as the whole of the IKN dwarf itself. While these fractions are much higher than in the Milky Way halo, we have previously found a similarly high ratio of metal-poor GCs to field stars in the Fornax dSph. The overall abundance patterns in the WLM GC are similar to those observed for GCs in the Fornax dSph: the [Ca/Fe] and [Ti/Fe] ratios are super-Solar at about +0.3 dex, while [Mg/Fe] is less elevated than [Ca/Fe] and [Ti/Fe]. The [Na/Fe] ratio is similar to the averaged [Na/Fe] ratios in Milky Way GCs, but higher (by ~2σ) than those of Milky Way halo stars. Iron-peak (Mn, Sc, Cr) and heavy elements (Ba, Y, La) generally follow the trends seen in the Milky Way halo.
Conclusions. The GCs in the WLM and IKN dwarf galaxies resemble those in the Fornax dSph by being significantly more metal-poor than a typical halo GC in the Milky Way and other large galaxies. They are also substantially more metal-poor than the bulk of the field stars in their parent galaxies. It appears that only a small fraction of the Milky Way GC system could have been accreted from galaxies similar to these dwarfs. The relatively high Na abundance in the WLM GC suggests that the [Na/O] anti-correlation is present in this cluster, while the high ratios of metal-poor GCs to field stars in the dwarfs are in tension with GC formation scenarios that require GCs to have lost a very large fraction of their initial mass.
Key words: methods: data analysis / galaxies: star clusters: individual: WLM GC / galaxies: star clusters: individual: IKN-5 / galaxies: abundances
Based on observations made with ESO telescopes at the La Silla Paranal Observatory under programme ID 077.B-0354(A), and at the W. M. Keck Observatory, which is operated as a partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration.
Tables 1 and 2 are available in electronic form at http://www.aanda.org
© ESO, 2014
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