Correlation between the distribution of the hydrogen volume density (n_H) derived from the Leike et al. (2020) 3D dust reconstruction and ¹²CO emission across distances and radial velocities as quantified by the projected Rayleigh statistic (V) for the 4 × 3 regions shown in Fig. 6. The vertical and horizontal dashed lines correspond to the distances and radial velocity ranges defined in Fig. 4. The circle marks the pair of distance and velocity channels with the highest global V, which are presented in Fig. 6.