Column density maps of HCO⁺, HCN, ¹³CO, HNC, and N₂H⁺, and molecular hydrogen column density map derived from Hi-GAL dust continuum emission. The thick white contours in each panel outline the column densities we used to construct the N-PDFs, and the thin white contours mark the optimal column density threshold (N_min for the optimal power-law fit) for the whole filament. The red contours in the dense gas molecular line panels mark N_min for the power law for the sub-regions (see Sect. 3.3). The green polygon in the Hi-GAL panel outlines the area we used to construct the N-PDFs from the dense gas tracers and continuum emission in the following sections. The beam of the column density maps (43′′ for Hi-GAL, 46′′ for ¹³CO, and 32′′ for the other panels) is marked in the bottom left of each panel. The polygons in the HCO⁺ panel and ellipses in the HCN panel are the same as in Fig. 2.