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The structure of star clusters in the outer halo of M31

Tanvir, N. R. ; Mackey, A. D. ; Ferguson, A. M. N. ; Huxor, A. ; Read, J. I. ; Lewis, G. F. ; Irwin, M. J. ; Chapman, S. ; Ibata, R. ; Wilkinson, M. I. ; McConnachie, A. W. ; Martin, N. F. ; Davies, M. B. ; Bridges, T. J.

In: Monthly Notices of the Royal Astronomical Society, 2012, vol. 422, no. 1, p. 162-184

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    Titre
    • The structure of star clusters in the outer halo of M31
    Auteur
    • Tanvir, N. R.. Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH
    • Mackey, A. D.. Research School of Astronomy & Astrophysics, The Australian National University, Mount Stromlo Observatory, Cotter Road, Weston Creek, ACT 2611, Australia
    • Ferguson, A. M. N.. Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ
    • Huxor, A.. Astronomisches Rechen-Institut, Universität Heidelberg, Mönchhofstrasse 12-14, 69120 Heidelberg, Germany
    • Read, J. I.. Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH
    • Lewis, G. F.. Sydney Institute for Astronomy, School of Physics, A28, The University of Sydney, NSW 2006, Australia
    • Irwin, M. J.. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA
    • Chapman, S.. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA
    • Ibata, R.. Observatoire Astronomique, Université de Strasbourg, CNRS, 11 rue de l'Université, F-67000 Strasbourg, France
    • Wilkinson, M. I.. Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH
    • McConnachie, A. W.. NRC Herzberg Institute of Astrophysics, 5071 West Saanich Road, British Columbia, Victoria V9E 2E7, Canada
    • Martin, N. F.. Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany
    • Davies, M. B.. Lund Observatory, Box 43, SE221 00 Lund, Sweden
    • Bridges, T. J.. Department of Physics, Queen's University, Kingston, Ontario K7L 3N6, Canada
    Type de document
    • Postprint
    Langue
    • Anglais
    Publié dans
    • Monthly Notices of the Royal Astronomical Society, 2012, vol. 422, no. 1, p. 162-184. Blackwell Publishing Ltd
    Autre version électronique
    Identifiant OAI-PMH
    • oai:doc.rero.ch:292782
    Summary
    We present a structural analysis of halo star clusters in M31 based on deep Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) imaging. The clusters in our sample span a range in galactocentric projected distance from 13 to 100 kpc and thus reside in rather remote environments. Ten of the clusters are classical globulars, whilst four are from the Huxor et al. population of extended, old clusters. For most clusters, contamination by M31 halo stars is slight, and so the profiles can be mapped reliably to large radial distances from their centres. We find that the extended clusters are well fit by analytic King profiles with ∼20 parsec core radii and ∼100 parsec photometric tidal radii, or by Sérsic profiles of index ∼1 (i.e. approximately exponential). Most of the classical globulars also have large photometric tidal radii in the range 50-100 parsec; however, the King profile is a less good fit in some cases, particularly at small radii. We find 60 per cent of the classical globular clusters exhibit cuspy cores which are reasonably well described by Sérsic profiles of index ∼2-6. Our analysis also reinforces the finding that luminous classical globulars, with half-light radii <10 parsec, are present out to radii of at least 100 kpc in M31, which is in contrast to the situation in the Milky Way where such clusters (other than the unusual object NGC 2419) are absent beyond 40 kpc