ST (Nature 493, 62-65)
A vast, thin plane of corotating dwarf galaxies orbiting the Andromeda galaxyIbata, et al
Dwarf satellite galaxies are thought to be the remnants of the population of primordial structures that coalesced to form giant galaxies like the MW. It has previously been suspected that dwarf galaxies may not be isotropically distributed around the Galaxy (from its correlation to H i emission, which may form coplanar groups [?]). The apparent planar distribution of satellites is not predicted within standard cosmology, and cannot simply represent a memory of past coherent accretion. Report existent of a planar subgroup of satellites in And (M31), comprising about half of the population [of what? satellites?]. The structure is at least 400 kpc in diameter, but also extremely thin, with a perpendicular scatter of <14.1 kpc. Radial velocity measurements reveal that the satellites in this structure have the same sense of rotation about their host. This shows conclusively that substantial numbers of dwarf satellite galaxies share the same dynamical orbital properties and direction of angular momentum. Intriguingly, the plane identified is approximately aligned with the pole of MW's disk, and with the vector between the MW and And.
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