  It has been suggested that the satellite galaxies of the Milky Way reside in
a highly-flattened, kinematically-coherent plane called Disk of Satellites
(DoS). The origin of the DoS, however, has been hotly debated, and a number of
conflicting claims have been reported in the literature on whether or not the
DoS is consistent with predictions from the standard Lambda Cold Dark Matter
($\Lambda$CDM) cosmological model. Here we investigate this issue by comparing
a high-resolution, hydrodynamic $\Lambda$CDM simulation of a Milky Way sized
galaxy with its dark matter only counterpart. We find the following results:
(1) The abundance and distribution of satellite galaxies around a host galaxy
is significantly different in the hydro simulation compared to its N-body
counterpart; (2) No clear coherent rotation is found in the satellite system,
as the fractions of corotating and counter-corotating satellites remain
comparable across cosmic time; (3) The satellite distribution evolves
significantly with time, from nearly isotropic at high redshift to anisotropic
at the present day; (4) The DoS properties strongly depend on sample selection
and plane identification methods. Our results imply that the spatially-thin and
coherently-rotating DoS reported in Milky Way and other galaxies may be a
selection effect of small sample size.
