Young accreted globular clusters in the outer halo of M31

A. D. Mackey*, A. P. Huxor, A. M. N. Ferguson, M. J. Irwin, J. Veljanoski, A. W. McConnachie, R. A. Ibata, G. F. Lewis, N. R. Tanvir

*Awdur cyfatebol y gwaith hwn

    Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid


    We report on observations of two newly discovered globular clusters in the outskirts of M31 made using the Gemini Multi-Object Spectrograph (GMOS) instrument on Gemini North. These objects, PAndAS-7 (PA-7) and PAndAS-8 (PA-8), lie at a galactocentric radius of approximate to 87 kpc and are projected, with separation approximate to 19 kpc, on to a field halo substructure known as the South-West Cloud. We measure radial velocities for the two clusters which confirm that they are almost certainly physically associated with this feature. Colour-magnitude diagrams reveal strikingly short, exclusively red horizontal branches in both PA-7 and PA-8; both also have photometric [Fe/H] = -1.35 +/- 0.15. At this metallicity, the morphology of the horizontal branch is maximally sensitive to age, and we use the distinctive configurations seen in PA-7 and PA-8 to demonstrate that both objects are very likely to be at least 2 Gyr younger than the oldest Milky Way globular clusters. Our observations provide strong evidence for young globular clusters being accreted into the remote outer regions of M31 in a manner entirely consistent with the established picture for the Milky Way, and add credence to the idea that similar processes play a central role in determining the composition of globular cluster systems in large spiral galaxies in general.

    Iaith wreiddiolSaesneg
    Tudalennau (o-i)281-293
    Nifer y tudalennau13
    CyfnodolynMonthly Notices of the Royal Astronomical Society
    Rhif cyhoeddi1
    Dynodwyr Gwrthrych Digidol (DOIs)
    StatwsCyhoeddwyd - Chwef 2013

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