The co-planarity of satellite galaxies delivered by randomly aligned
  cold mode accretion streams
  Recent observations have shown that the majority of the Andromeda galaxy's
satellites are aligned in a thin plane. On the theoretical side it has been
proposed that galaxies acquire their gas via cold streams. In addition,
numerical simulations show that the same streams also deliver gas clumps which
could potentially develop into satellite galaxies. Assuming that cold streams
are a major source of satellite systems around galaxies we calculate the
probabilities in two different models to find a certain fraction of satellites
within a thin plane around the central galaxy of the host halo with and without
having the same sense of rotation. Using simple geometrical considerations and
adopting a random orientation of the streams we demonstrate that the vast thin
disk of satellites detected around Andromeda can naturally be explained within
this framework. In fact, without any satellite scattering, two streams would
lead to too many satellites in the thin plane, compared with the observations.
Three streams reproduce the observations very well. Natural implications from
our model are that all massive galaxies should have a thin plane of satellites
and that the satellites should naturally distribute themselves not only into a
single plane but into several inclined ones. We estimate the effect of
additional satellites accreted from random directions and find it to be of
minor relevance for a mild inflow of satellites from random directions.
