Total and molecular hydrogen column density maps. Left: High-resolution N(H) total gas column density map obtained from the Herschel flux maps of M33 with 18.2″ angular resolution (indicated by the circle in the lower left corner) using the β map from Tabatabaei et al. (2014). Values below and above a minimum and maximum threshold (10¹⁸ cm⁻² and 10²² cm⁻², respectively) are blanked. Right: High-resolution H₂ column density map derived from the total N(H) map by subtracting the H I component. In both maps, the CO contour levels 3 and 6σ of the CO map (Fig. A.1 in Appendix A) are shown.