Test-particle streams from Fig. 9–11 with the frequencies ΔΩ_r−ΔΩ_φ (top panels) and angles Δθ_r−Δθ_φ (middle panels) and Δθ_r−Δθ_ϑ (bottom panels), computed using an NFW potential that has the same slope at a fixed radius as the limiting spherical isochrone potential (see Fig. C.1). The colours represent the energy gradient in the NFW potential. The panels have been centred on the progenitor position. The insets indicate the fitted slopes for the approximate potential. The errors were found by bootstrapping the fit 200 times.