Stacked spectra of ¹³CO (J = 1–0) emission corresponding to the “inside” (red) and “outside feedback” zones (blue) for different choices of MSX at 8.28 μm flux density (designated as “thre” in units of W/(m⁻²⋅ sr) in the top–left of each subplot) in the four regions: W5-E1, W5-M, W5-W1, and W5-W2, as described in Fig. 8. The red solid and blue dotted lines in all the subplots correspond to the position of peak emission of the average stacked spectra inside and outside the feedback zone with MSX 8.28 μm flux densities above and below the variation threshold. The velocity interval between the two peak lines is expressed in “ dv” ( km s⁻¹) on the top–left of each subplot. (a) W5-E1, (b) W5-M, (c) W5-W1, (d) W5-W2.