The spatial distribution of Milky Way satellites, gaps in streams and
  the nature of dark matter
  The spatial distribution of Milky Way (MW) subhaloes provides an important
set of observables for testing cosmological models. These include the radial
distribution of luminous satellites, planar configurations, and the abundance
of dark subhaloes whose existence or absence is key to distinguishing amongst
dark matter models. We use the COCO $N$-body simulations of cold dark matter
(CDM) and 3.3keV thermal relic warm dark matter (WDM) to predict the satellite
spatial distribution. We demonstrate that the radial distributions of CDM and
3.3keV-WDM luminous satellites are identical if the minimum pre-infall halo
mass to form a galaxy is $>10^{8.5}$$\mathrm{M}_{\odot}$ The distribution of
dark subhaloes is significantly more concentrated in WDM due to the absence of
low mass, recently accreted substructures that typically inhabit the outer
parts of a MW halo in CDM. We show that subhaloes of mass
$[10^{7},10^{8}]$$\mathrm{M}_{\odot}$ and within 30kpc of the centre are the
stripped remnants of larger haloes in both models. Therefore their abundance in
WDM is $3\times$ higher than one would anticipate from the overall WDM subhalo
population. We estimate that differences between CDM and WDM
concentration--mass relations can be probed for subhalo--stream impact
parameters $<2$kpc. Finally, we find that the impact of WDM on planes of
satellites is likely negligible. Precise predictions will require further work
with high resolution, self-consistent hydrodynamical simulations.
