Modulus of the gradient of the rest-mass density (in logarithmic scale) for models FMH1 (left panels) and FMH1_m4 (right panels). The upper panels show the entire grid, while in the bottom ones we show a zoom-in in the 0.3–0.9 pc region. The modulus of the gradient of the rest-mass density highlights the location of steep sound waves and shock waves. The black squares highlight the triple point associated with the incident/reflected/Mach shocks in the jet-ambient transition surface (for details, see Sect. 4.3). In the bottom panels, the contours represent the tracer at the level f = 0.9, showing the transition between the inner jet and the shear layer.