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E.K. Grebel, A. Koch, N. Sambhus (University of Basel)
The unexpected, highly anisotropic distribution and apparent alignment of the Galactic satellites in polar great planes has been interpreted as a possible indication of common orbital planes, of a prolate Galactic dark halo, or as possible signature of infall along filaments. If such planes have any physical meaning, one would also expect them around other massive galaxies. The dwarf satellite system of M31 is the only nearby system for which we currently have sufficiently accurate distances to study the three-dimensional satellite distribution. Moreover, the M31 companions resemble those of the Milky Way in terms of numbers and distances. Here we present the discovery of a polar great plane of M31 early-type satellites, which has a statistical significance of 99.3 percent and points toward M33 and the M81 group. The r.m.s. distance of the early-type dwarf galaxies from this plane is 16 kpc. The giant Andromeda stream does not lie in this polar plane. In contrast to the Milky Way, there is no clear evidence for a Holmberg effect in the M31 dwarf satellite distribution. We test the physical reality of the plane via orbit calculations. Different scenarios for the origin and implications of such satellite anisotropies are discussed.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.