The green color scale shows the normalized kernel density distribution of σv and N _col in AG14, with the contour levels set on [0.1, 0.3, 0.5, 0.7, 0.9]. The same data are shown for AG351 with the dashed contours and for AG354 with solid contours (taken from Redaelli et al. 2021; the N _col values have been corrected by a factor ﹩\sqrt{\pi }﹩; see text for details). The horizontal blue solid and red dashed–dotted lines represent the sound speed and the thermal broadening of o‐H₂D⁺, respectively, both at 10 K.