The Orbital Poles of Milky Way Satellite Galaxies: A Rotationally Supported Disk of Satellites

We use available proper-motion measurements of Milky Way (MW) satellite galaxies to calculate their orbital poles and projected uncertainties. These are compared with a set of recent cold dark matter (CDM) simulations tailored specifically to solve the MW satellite problem. We show that the CDM satellite orbital poles are fully consistent with being drawn from a random distribution, while the MW satellite orbital poles indicate that the "disk of satellites" of the Milky Way is rotationally supported. Furthermore, a bootstrap analysis of the spatial distribution of theoretical CDM satellites also shows that they are consistent with being randomly drawn. The theoretical CDM satellite population thus shows a significantly different orbital and spatial distribution from that of the MW satellites, most probably indicating that the majority of the latter are of tidal origin rather than being dark matter-dominated substructures. A statistic is presented that can be used to test a possible correlation of satellite galaxy orbits with their spatial distribution.