Correlation between the dense gas fraction and the strength of fast shocks. (a) Integrated intensity ratio map of H¹³CN/¹³CO(1–0). The black contour is drawn at 0.06 and the blue contour at 0.12. The labels 3, 6, and 7 mark the same GMCs as in Fig. 5c. (b) Correlation between H¹³CN/¹³CO(1–0) and SiO(2–1)/¹³CO(1–0). The blue points mark the ratios from pixels with a spatial resolution equaling the beam size. The solid gray line shows the result of a linear fit to the blue points.