Distribution of halo stars (red filled circles) in the angular momentum-radial action space. For comparison, we also plot all the stars in the sample (mostly disc stars) with cyan symbols and with a histogram of point density in the crowded region where orbits are nearly circular (J_R ~ 0, J_ϕ ~ J_⊙). The cyan points at large J_R and/or at small or retrograde J_ϕ, although located in the region where the halo dominates, in practice have uncertainties that are too large and thus fail to pass the criterion given by Eq. (11); they are therefore not part of the dynamically selected halo. The yellow star marks the position of the Sun in this diagram. We show 16th–84th percentile error bars, computed as in Sect. 3.4, for all the halo stars with fractional error on J_R smaller than 90%; instead, we plot as black empty circles the other halo stars for visualization purposes.