a) Column density map (in cm^-2) of the DR21 ridge with the crest as black dots and the black N_H2 = 10²³ cm^-2 contour. Note that white pixels are undefined because of saturation. Blue ellipses give the position and extent (FWHM = semi-axes) of the Motte et al. (2007) dense cores. b), c) Radial column density profiles towards the crest locations b and c marked in yellow/blue in a). The radial profiles are averaged over the marked crest dots. The yellow areas show the  ± 1σ ranges.