Bringing the Galaxy's dark halo to life
  We present a new method to construct fully self-consistent equilibrium models
of multi-component disc galaxies similar to the Milky Way. We define
distribution functions for the stellar disc and dark halo that depend on phase
space position only through action coordinates. We then use an iterative
approach to find the corresponding gravitational potential. We study the
adiabatic response of the initially spherical dark halo to the introduction of
the baryonic component and find that the halo flattens in its inner regions
with final minor-major axis ratios $q$ = 0.75 - 0.95. The extent of the
flattening depends on the velocity structure of the halo particles with
radially biased models exhibiting a stronger response. In this latter case,
which is according to cosmological simulations the most likely one, the new
density structure resembles a "dark disc" superimposed on a spherical halo. We
discuss the implications of these results for our recent estimate of the local
dark matter density. The velocity distribution of the dark-matter particles
near the Sun is very non-Gaussian. All three principal velocity dispersions are
boosted as the halo contracts, and at low velocities a plateau develops in the
distribution of $v_z$. For models similar to a state-of-the-art Galaxy model we
find velocity dispersions around 155 km s$^{-1}$ for $v_z$ and the tangential
velocity, $v_\varphi$, and 140 - 175 km s$^{-1}$ for the in-plane radial
velocity, $v_R$, depending on the anisotropy of the model.
