Triangulum galaxy M 33. This image shows in plain green the edges of the coverage of the CO(2–1) survey on top of a Herschel 250 μm map (Xilouris et al. 2012) that traces cold dust. The green dotted limits correspond to the previous processed area in Gratier et al. (2010b). The 2′×40′ wide HerM33es strip, in white dots, is also the region where the CO(1–0) transition has been observed with the 30 m telescope. The purple limited areas (white lines in Fig. 1) are the H i-poor regions where we detect no H i above 10 K and inside which we can see that there is no strong 250 μm emission. The white ellipse represents a 7.2 kpc radius from the center.