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Letters to Nature

Nature 412, 49-52 (5 July 2001) | doi:10.1038/35083506; Received 9 February 2001; Accepted 4 May 2001

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A giant stream of metal-rich stars in the halo of the galaxy M31

Rodrigo Ibata1, Michael Irwin2, Geraint Lewis3, Annette M. N. Ferguson4 & Nial Tanvir5

  1. Observatoire de Strasbourg, 11, rue de l'Universite, F-67000 Strasbourg, France
  2. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
  3. Anglo-Australian Observatory, PO Box 296, Epping, New South Wales 1710, Australia
  4. Kapteyn Astronomical Institute, Postbus 800, 9700 AV Groningen, The Netherlands
  5. Physical Sciences, University of Hertfordshire, Hatfield AL10 9AB, UK

Correspondence to: Rodrigo Ibata1 Correspondence and requests for materials should be addressed to R.I. (e-mail: Email: ibata@astro.u-strasbg.fr).

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Recent observations have revealed streams of gas and stars in the halo of the Milky Way1, 2, 3 that are the debris from interactions between our Galaxy and some of its dwarf companion galaxies; the Sagittarius dwarf galaxy and the Magellanic clouds. Analysis of the material has shown that much of the halo is made up of cannibalized satellite galaxies2, 4, and that dark matter is distributed nearly spherically in the Milky Way. It remains unclear, however, whether cannibalized substructures are as common in the haloes of galaxies as predicted by galaxy-formation theory5. Here we report the discovery of a giant stream of metal-rich stars within the halo of the nearest large galaxy, M31 (the Andromeda galaxy). The source of this stream could be the dwarf galaxies M32 and NGC205, which are close companions of M31 and which may have lost a substantial number of stars owing to tidal interactions. The results demonstrate that the epoch of galaxy building still continues, albeit at a modest rate, and that tidal streams may be a generic feature of galaxy haloes.

  1. Observatoire de Strasbourg, 11, rue de l'Universite, F-67000 Strasbourg, France
  2. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
  3. Anglo-Australian Observatory, PO Box 296, Epping, New South Wales 1710, Australia
  4. Kapteyn Astronomical Institute, Postbus 800, 9700 AV Groningen, The Netherlands
  5. Physical Sciences, University of Hertfordshire, Hatfield AL10 9AB, UK

Correspondence to: Rodrigo Ibata1 Correspondence and requests for materials should be addressed to R.I. (e-mail: Email: ibata@astro.u-strasbg.fr).