Details of the dust temperature (left column), dust optical depth at 857 GHz (central column) and dark gas column density (right column) for the Chamaeleon (first line), Aquila-Ophiuchus flare (second line), Polaris flare (third line) and Taurus (fourth line). The temperature and optical depth maps are shown in log scale with a colour scale ranging from 15K (black) to 20K (red) and 1 × 10^-5 (black) to 3 × 10^-3 (red) respectively. The dark gas column density derived from the optical depth at 857 GHz (see Sect.4) and is shown in linear scale with a colour scale ranging from –3 (black) to 7 × 10²¹Hcm^-2 (red). The contours show the ¹²CO(J = 1 → 0) integrated intensity at 2, 10 and 20K km s^-1. The double line shows the limit of the CO surveys.