  The predicted abundance and properties of the low-mass substructures embedded
inside larger dark matter haloes differ sharply among alternative dark matter
models. Too small to host galaxies themselves, these subhaloes may still be
detected via gravitational lensing, or via perturbations of the Milky Way's
globular cluster streams and its stellar disk. Here we use the Apostle
cosmological simulations to predict the abundance and the spatial and velocity
distributions of subhaloes in the range 10^6.5-10^8.5 solar masses inside
haloes of mass ~ 10^12 solar masses in LCDM. Although these subhaloes are
themselves devoid of baryons, we find that baryonic effects are important.
Compared to corresponding dark matter only simulations, the loss of baryons
from subhaloes and stronger tidal disruption due to the presence of baryons
near the centre of the main halo, reduce the number of subhaloes by ~ 1/4 to
1/2, independently of subhalo mass, but increasingly towards the host halo
centre. We also find that subhaloes have non-Maxwellian orbital velocity
distributions, with centrally rising velocity anisotropy and positive velocity
bias which reduces the number of low-velocity subhaloes, particularly near the
halo centre. We parameterise the predicted population of subhaloes in terms of
mass, galactocentric distance, and velocities. We discuss implications of our
results for the prospects of detecting dark matter substructures and for
possible inferences about the nature of dark matter.
