How common is the Milky Way–satellite system alignment? |
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| Authors: | Noam I Libeskind Carlos S Frenk Shaun Cole Adrian Jenkins John C Helly |
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| Institution: | Racah Institute of Physics, Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904, Israel;Astrophysikalisches Institut Potsdam, An der Sternwarte 16, Potsdam 14482, Germany;Department of Physics, University of Durham, Science Laboratories, South Road, Durham DH1 3LE |
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| Abstract: | The highly flattened distribution of satellite galaxies in the Milky Way (MW) presents a number of puzzles. First, its polar alignment stands out from the planar alignments commonly found in other galaxies. Secondly, recent proper-motion measurements reveal that the orbital angular momentum of at least three, and possibly as many as eight, of the MW's satellites points (within 30° ) along the axis of their flattened configuration, suggesting some form of coherent motion. In this paper, we use a high-resolution cosmological simulation to investigate whether this pattern conflicts with the expectations of the cold dark matter model of structure formation. We find that this seemingly unlikely setup occurs often: approximately 35 per cent of the time, we find systems in which the angular momentum of three individual satellites points along, or close to, the short axis of the satellite distribution. In addition, in 30 per cent of the systems we find that the net angular momentum of the six best-aligned satellites lies within 35° of the short axis of the satellite distribution, as observed for the MW. |
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| Keywords: | galaxies: haloes galaxies: kinematics and dynamics Local Group cosmology: theory large-scale structure of Universe |
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