A) Specific angular momentum, L_z, as a function of the cylindrical radius, R, during the orbital migration of the BH. The large sky-blue arrows indicate the flow of time, t. The orange solid lines trace the expected values for the model galaxy. The curve in blue (red) shows the coordinates before (after) L_z has reached a maximum. The black lines indicate evolution at a constant L_z. The circles numbered 1 and 2 single out specific phases of evolution. B) Run of azimuthal velocity, v_ϕ, against radius, R. The axes have been shifted for clarity. The colour-coding for the other curves and symbols is as for (A).