Spectra along the west–east filament. Top: finding chart with a color scale showing the H¹³CO⁺ first-moment map and contours showing the 3.6 mm continuum in 4σ steps. The arrow indicates the pv cut from Fig. 7; the stars mark the positions where the spectra are extracted; and the main sources are labeled (see Fig. 3). Bottom: corresponding HCO + and H 13 CO spectra in black and red, respectively.