Left: topology of ℋ (3) on the R–V_θ plane of initial conditions, where V_θ = J_ϕ/R, p_R = 0, and ϕ = 90°. Right: dynamical maps on the same plane calculated for the time series J_ϕ(t). The shaded blue regions correspond to domains of initial conditions leading to orbits which go beyond 30 kpc (the region where our model is no longer applicable). The bar relates grey tones and the values of the spectral number N between 1 and 100 in logarithmic scale. All orbits with N> 100 are labelled in black. A typical orbit intersects this plane in two points corresponding to the minimum and maximum values of the coordinate R.