The rotationally stabilized VPOS and predicted proper motions of the
  Milky Way satellite galaxies
  The satellite galaxies of the Milky Way (MW) define a vast polar structure
(VPOS), a thin plane perpendicular to the MW disc. Proper motion (PM)
measurements are now available for all of the 11 brightest, `classical'
satellites and allow an updated analysis of the alignment of their orbital
poles with this spatial structure. The coherent orbital alignment of 7 to 9 out
of 11 satellites demonstrates that the VPOS is a rotationally stabilized
structure and not only a pressure-supported, flattened ellipsoid. This allows
us to empirically and model independently predict the PMs of almost all
satellite galaxies by assuming that the MW satellite galaxies orbit within the
VPOS. As a test of our method, the predictions are best met by satellites whose
PMs are already well constrained, as expected because more uncertain
measurements tend to deviate more from the true values. Improved and new PM
measurements will further test these predictions. A strong alignment of the
satellite galaxy orbital poles is not expected in dark matter based simulations
of galaxy formation. Coherent orbital directions of satellite galaxies are,
however, a natural consequence of tidal dwarf galaxies formed together in the
debris of a galaxy collision. The orbital poles of the MW satellite galaxies
therefore lend further support to tidal scenarios for the origin of the VPOS
and are a very significant challenge for the standard LCDM model of cosmology.
We also note that the dependence of the MW satellite speeds on Galactocentric
distance appear to map an effective potential with a constant velocity of
approximately 240 km/s to about 250 kpc. The individual satellite velocities
are only mildly radial.
