  In this work, we investigate the discovery potential of low-mass Galactic
dark matter (DM) subhaloes for indirect searches of DM. We use data from the
Via Lactea II (VL-II) N-body cosmological simulation, which resolves subhaloes
down to $\mathcal{O}(10^4)$ solar masses and it is thus ideal for this purpose.
First, we characterize the abundance, distribution and structural properties of
the VL-II subhalo population in terms of both subhalo masses and maximum
circular velocities. Then, we repopulate the original simulation with millions
of subhaloes of masses down to about five orders of magnitude below the minimum
VL-II subhalo mass (more than one order of magnitude in velocities). We compute
subhalo DM annihilation astrophysical "J-factors" and angular sizes for the
entire subhalo population, by placing the Earth at a random position but at the
right galactocentric distance in the simulation. Thousands of these
realizations are generated in order to obtain statistically meaningful results.
We find that some nearby low-mass Galactic subhaloes, not massive enough to
retain stars or gas, may indeed yield DM annihilation fluxes comparable to
those expected from other, more massive and acknowledgeable DM targets like
dwarf satellite galaxies. Typical angular sizes are of the order of the degree,
thus subhaloes potentially appearing as extended sources in gamma-ray
telescopes, depending on instrument angular resolution and sensitivity. Our
work shows that low-mass Galactic subhaloes with no visible counterparts are
expected to play a relevant role in current and future indirect DM search
searches and should indeed be considered as excellent DM targets.
