Title: The co-planarity of satellite galaxies delivered by randomly aligned cold mode accretion 
streams

Abstract:
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 
satellites. 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 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. We estimated the effect of additional satellites accreted 
from random directions and found it to be of minor relevance.