  The annihilation of dark matter particles in the halo of galaxies may end up
into gamma rays, which travel almost unperturbed till to their detection at
Earth. This annihilation signal can exhibit an anisotropic behavior quantified
by the angular power spectrum, whose properties strongly depend on the dark
matter distribution and its clumpiness. We use high resolution pure dark matter
N-body simulations to quantify the contribution of different components (main
halo and satellites) to the global signal as a function of the analytical
profile adopted to describe the numerical results. We find that the smooth main
halo dominates the angular power spectrum of the gamma-ray signal up to quite
large multipoles, where the sub-haloes anisotropy signal starts to emerge, but
the transition multipole strongly depends on the assumed radial profile. The
extrapolation down to radii not resolved by current numerical simulations can
affect both the normalization and the shape of the gamma-ray angular power
spectrum. For the sub-haloes described by an asymptotically cored dark matter
distribution, the angular power spectrum shows an overall smaller normalization
and a flattening at high multipoles. Our results show the criticality of the
dark matter density profile shape in gamma-ray anisotropy searches, and
evaluate quantitatively the intrinsic errors occurring when extrapolating the
dark matter radial profiles down to spatial scales not yet explored by
numerical simulations.
