Vertical squared velocity dispersion on vertical direction profiles binned in |z|, for the five sub-samples in the north (upper panel), and in the south (bottom panel). The colour code per sector is the same as in Fig. 3. Black curves represent the best fit following Eq. (6) and the parameters given in Table 4, plotted at the three R values (7.54, 8.34, and 9.14 kpc from the highest to the lowest).