Intensity, intensity gradients, and relative orientation angle maps from the synthetic observations of the Clark et al. (2018) simulations. In contrast with the simulations presented in Sect. 3, the synthetic observation do not include the 100-K HI background emission. Left panels: HI (teal) and ¹³CO emission (red) in the velocity channels with the largest spatial correlation, as inferred from the V values shown in Fig. 6. Middle left panels: norm of the gradient of the HI intensity map in the indicated velocity channel. Middle right panels: norm of the gradient of the ¹³ CO intensity map in the indicated velocity channel. Right panels: relative orientation angle ϕ, Eq. (1), between the gradients of the HI and ¹³CO intensity maps in the indicated velocity channels. The white color in the ϕ map corresponds to areas with no significant gradient in either tracer. The square indicates the block, selected from a 7 × 7 spatial grid, with the largest values of V. Top and bottom panels: face-on and edge-on synthetic observations, respectively.