Counter-Orbiting Tidal Debris as the Origin of the MW DoS
  The Milky Way satellite galaxies show a phase-space distribution that is not expected from the standard scenario of galaxy formation. This is a strong hint at them being of tidal origin, which would naturally explain their spacial distribution in a disc of satellites. It is shown that also their orbital directions can be reproduced with the debris of galaxy collisions. Both co- and counter-orbiting satellites are formed naturally in merger and fly-by interactions. 
Marcel S. Pawlowski
astro-ph.GA astro-ph.CO