Left panels: integrated intensity contours of the HCO⁺(1–0), HCN(1–0), HNC(1–0), and N₂H⁺(1–0) overlaid on the molecular hydrogen column density map derived from fitting Hi-GAL 160, 250, 350, and 500 μm continuum maps (Zucker et al. 2018). Contour levels are 3, 9, 15, 25, and 35 times of the respective σ of each integrated intensity map. The noise level of each panel from top to bottom: 0.28, 0.40, 0.22, and 0.29 K km s⁻¹, respectively. The integral velocity range for each line is labeled in each panel in units of km s⁻¹. The polygons in the HCO⁺(1–0) panel outline the four sub-regions, A, B, C, and D, which we studied in Sect. 3.3. The thick black contour in each panel traces the 5σ level of the GRS ¹³CO(1–0) integrated intensity. The red ellipses mark the emissions that are at a different distance and not associated with the filament. The beam of the molecular line emission (32′′) is marked in the bottom left of each panel. Right panels: average spectra of the dense gas tracers across the filament. The thick black spectra are HCO⁺ (1–0), HCN(1–0), HNC(1–0), and N₂H⁺(1–0) lines, respectively. The thin blue spectra are the ¹³C isotopologues that are scaled up by a factor of ten. The shades mark the integral velocity range for each line.