Median V_z distribution of disk stars: (a) projected in the X − Y plane from the N-body simulation of a galactic disk perturbed by a satellite comparable in mass to the Sagittarius dwarf galaxy; (b) from the dashed rectangular region of the left plot, with the Sun placed at the interface of underdense (blue) and overdense (red) region in velocity space (as seen from the velocity maps in Fig. 2), showing a maximum amplitude close to 4 km s⁻¹, comparable to that of the OB stars as seen from Fig. 2.