Top panel: predicted centroid velocities in units of the total gas speed for a PV along the jet, for the same two models shown in Fig. 8: cone (in red) and half-sphere (in black). The bottom solid curves are for a pure outward parallel flow (cosα = 0), top curves for a pure outward perpendicular flow (cosα = 1), and middle curves for an intermediate situation (V_∥/V_⊥ = 1.3, cosα = 0.6). Bottom panel: observed H₂ 1–0 S(1) centroid velocities in a PV along the jet axis (symbols with error bars, from Fig. 4) compared with predictions for the conical model. Dashed curve: V_⊥ = 20 km s^-1 and cosα = 0.6; dash-dotted curve: V_⊥ =  −5 km s^-1 and V_∥ = 0; solid curve: V_⊥ =  + 10 km s^-1 and V_∥ = 0.