Peak velocity of the Gaussian fit of the ¹³CO data (top panel) and the HISA data (bottom panel), respectively. The HISA are extracted by using a second order polynomial to estimate the background emission. The black contours indicate the integrated ¹³CO emission at levels of 5 K km s⁻¹. The polygons mark the eastern (around l = 36.5°) and western (around l = 34°) subregions, for which we present the histograms of the peak velocities in Fig. 10.