Thin disk of co-rotating dwarfs: a fingerprint of dissipative (mirror)
  dark matter?
  Recent observations indicate that about half of the dwarf satellite galaxies
around M31 orbit in a thin plane approximately aligned with the Milky Way. It
has been argued that this observation along with several other features can be
explained if these dwarf satellite galaxies originated as tidal dwarf galaxies
formed during an ancient merger event. However if dark matter is collisionless
then tidal dwarf galaxies should be free of dark matter - a condition that is
difficult to reconcile with observations indicating that dwarf satellite
galaxies are dark matter dominated. We argue that dissipative dark matter
candidates, such as mirror dark matter, offer a simple solution to this puzzle.
