Tilt-angle α_Rz as a function of height above the Galactic plane for the dynamically selected stellar halo (red circles, left panel) and the metallicity selected stellar halo (yellow circles, right panel). Each bin in z contains roughly the same number of stars (≃185 and ≃ 175 respectively for the two halos). The value of α_Rz and its uncertainty are estimated using a multivariate normal model as in Sect. 4.3, while the error bars in z indicate the 16th–84th percentile of the z distribution in that bin. The blue solid line indicates a model in which the halo’s velocity ellipsoid is aligned with the spherical coordinates.