The globular cluster system of the Milky Way: accretion in a
  cosmological context
  We examine the significance of a planar arrangement in the spatial
distribution of the Milky Way's globular clusters (GCs). We find that, when
separated on the basis of horizontal branch morphology and metallicity, the
outer-most canonical young halo GC sample (at galactocentric radii in excess of
10 kpc) exhibit an anisotropic distribution that may be equated to a plane (24
+/- 4) kpc thick (rms) and inclined at 8 degrees +/- 5 degrees to the polar
axis of the Milky Way disk. To quantify the significance of this plane we
determine the fraction of times that an isotropic distribution replicates the
observed distribution in Monte-Carlo trials. The plane is found to remain
significant at the >95% level outside a galactocentric radius of 10 kpc, inside
this radius the spatial distribution is apparently isotropic. In contrast, the
spatial distribution of the old halo sample outside 10 kpc is well matched by
an isotropic distribution. The plane described by the outer young halo globular
clusters is indistinguishable in orientation from that presented by the
satellite galaxies of the Milky Way. Simulations have shown that the planar
arrangement of satellites can arise as filaments of the surrounding large scale
structure feed into the Milky Way's potential. We therefore propose that our
results are direct observational evidence for the accreted origin of the outer
young halo globular cluster population. This conclusion confirms numerous lines
of evidence that have similarly indicated an accreted origin for this set of
clusters from the inferred cluster properties.
