The orbital phase space of contracted dark matter halos
  We study the orbital phase-space of dark matter (DM) halos in the AURIGA
suite of cosmological hydrodynamics simulations of Milky Way analogues. We
characterise halos by their spherical action distribution, a function of the
specific angular momentum, and the radial action, of the DM particles. By
comparing DM-only and hydrodynamical simulations of the same halos, we
investigate the contraction of DM halos caused by the accumulation of baryons
at the centre. We find a small systematic suppression of the radial action in
the DM halos of the hydrodynamical simulations, suggesting that the commonly
used adiabatic contraction approximation can result in an underestimate of the
density by ~ 8%. We apply an iterative algorithm to contract the AURIGA DM
halos given a baryon density profile and halo mass, recovering the true
contracted DM profiles with an accuracy of ~15%, that reflects halo-to-halo
variation. Using this algorithm, we infer the total mass profile of the Milky
Way's contracted DM halo. We derive updated values for the key astrophysical
inputs to DM direct detection experiments: the DM density and velocity
distribution in the Solar neighbourhood.
