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A panoramic view of the Southern quadrant of the Andromeda galaxy outer halo

Published online by Cambridge University Press:  01 December 2006

Nicolas F. Martin ,
Rodrigo A. Ibata  and
Mike J. Irwin
Nicolas F. Martin
Affiliation:
Max-Planck Institute für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany email: martin@mpia-hd.mpg.de
Rodrigo A. Ibata
Affiliation:
Observatoire de Strasbourg, 11 rue de l'Université, F-67000 Strasbourg, France email: ibata@astro.u-strasbg.fr
Mike J. Irwin
Affiliation:
Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, U.-K. email: mike@ast.cam.ac.uk
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Abstract

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How clumpy are galactic halos? Recent observations around both the Milky Way and the Andromeda galaxy (M31) have revealed numerous faint stellar streams and dwarf galaxies, leading to the belief that more of these may yet remain undetected. In this contribution, we present the map produced from the Megacam/CFHT survey that our group has undertaken in the outer halo of M31 and that, for the first time, gives a deep panoramic view of a significant region of the outer halo of a spiral galaxy. This panoramic survey, which covers ∼ 60 sq. deg. of the southern quadrant of the M31 halo, extends the WFC/INT survey of the inner halo (Ferguson et al. 2002) from a projected distance of ∼ 50 to ∼ 150 kpc. It is deep enough to cover three magnitudes below the tip of the red giant branch of stellar populations at the distance of M31. The survey reveals:

  • • Three faint dwarf galaxies with absolute magnitudes in the range -7.3 < M_V < -6.4 and the most remote M31 globular cluster at a projected distance of ∼ 120 kpc from M31 (see Martin et al. 2006 for more details).

  • • That the giant stream of Ibata et al. (2001) covers a much wider area than previously expected from shallower surveys, has an apocenter at 125±25 kpc from M31 and is probably due to the accretion of a small disk galaxy.

  • • A new stellar stream or shell approximately perpendicular to the minor axis of M31 at a projected distance of 120 kpc and with a metallicity of [Fe/H] ∼ -1.5 (assuming it is at the distance of M31).

  • • A new stellar stream along the ma jor axis of M31 that extends to at least 100 kpc from M31 with [Fe/H] ∼ -1.3 (once again assuming it is at the distance of M31).

  • • Regions void of any stellar structure brighter than 34-35 mag/arcsec2 at a distance of 100 to 130 kpc from M31.

The survey shows that the outer halo of the Andromeda galaxy is very structured, in qualitative agreement with recent cosmological simulations (e.g. Bullock & Johnston, 2005).

Keywords

galaxies: evolutiongalaxies: halosgalaxies: individual (M31)galaxies: structuregalaxies: Local Group
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 2 , Symposium S241: Stellar Populations as Building Blocks of Galaxies , December 2006 , pp. 357 - 358
Copyright
Copyright © International Astronomical Union 2007

References

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