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Study of the Sextans dwarf spheroidal galaxy from the DART Ca ii triplet survey

Battaglia, G. ; Tolstoy, E. ; Helmi, A. ; Irwin, M. ; Parisi, P. ; Hill, V. ; Jablonka, P.

In: Monthly Notices of the Royal Astronomical Society, 2011, vol. 411, no. 2, p. 1013-1034

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    Titre
    • Study of the Sextans dwarf spheroidal galaxy from the DART Ca ii triplet survey
    Auteur
    • Battaglia, G.. European Organization for Astronomical Research in the Southern Hemisphere, K. Schwarzschild-Str. 2, 85748 Garching, Germany
    • Tolstoy, E.. Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, the Netherlands
    • Helmi, A.. Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, the Netherlands
    • Irwin, M.. Institute of Astronomy, Madingley Road, Cambridge CB03 0HA
    • Parisi, P.. INAF - Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna, via Gobetti 101, 40129 Bologna, Italy
    • Hill, V.. Université de Nice Sophia-Antipolis, CNRS, Observatoire de la Côte d'Azur, Laboratoire Cassiopée, B.P. 4229, 06304 Nice cedex 4, France
    • Jablonka, P.. Observatoire de Genève, Laboratoire d'Astrophysique de l'Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1290 Sauverny, Switzerland
    Type de document
    • Postprint
    Langue
    • Anglais
    Publié dans
    • Monthly Notices of the Royal Astronomical Society, 2011, vol. 411, no. 2, p. 1013-1034. Blackwell Publishing Ltd
    Autre version électronique
    Identifiant OAI-PMH
    • oai:doc.rero.ch:289550
    Summary
    We use Very Large Telescope (VLT)/Fibre Large Array Multi Element Spectrograph (FLAMES) intermediate-resolution (R∼ 6500) spectra of individual red giant branch stars in the near-infrared Ca ii triplet (CaT) region to investigate the wide-area metallicity properties and internal kinematics of the Sextans dwarf spheroidal galaxy (dSph). Our final sample consists of 174 probable members of Sextans with accurate line-of-sight velocities (±2 km s−1) and CaT [Fe/H] measurements (±0.2 dex). We use the Mg i line at 8806.8 Å as an empirical discriminator for distinguishing between probable members of the dSph (giant stars) and probable Galactic contaminants (dwarf stars). Sextans shows a similar chemodynamical behaviour to other Milky Way dSphs, with its central regions being more metal rich than the outer parts and with the more metal-rich stars displaying colder kinematics than the more metal-poor stars. Hints of a velocity gradient are found along the projected major axis and along an axis at position angle (PA) = 191°, however, a larger and more spatially extended sample may be necessary to pin down the amplitude and direction of this gradient. We detect a cold kinematic substructure at the centre of Sextans, consistent with being the remnant of a disrupted very metal poor stellar cluster. We derive the most extended line-of-sight velocity dispersion profile for Sextans, out to a projected radius of 1°.6. From Jeans modelling of the observed line-of-sight velocity dispersion profile we find that this is consistent with both a cored dark matter halo with large core radius and cuspy halo with low concentration. The mass within the last measured point is in the range 2-4 × 108 M⊙, giving very large mass-to-light ratios, from 460 to 920 (M/L)V, ⊙