The left main panel represents the H¹³CO⁺ emission obtained with the PdBI and zero-spacings. The gray scale shows integrated intensity around the v_lsr, between 14.5–15.5 km s^-1. Blue contours correspond to integrated intensity between 13.5–14.5 km s^-1 and red contours show integrated intensity between 15.5–16.5 km s^-1. Contours go from 5 × rms noise and increase in steps of 3 × rms noise. For comparison, the black dashed contour shows the 30% of the peak intensity of the 3 mm continuum map. Fully sampled spectra are extracted in two cuts following two filamentary structures indicated by long arrows, where the position corresponding to each spectra are shown in the upper right corner. These cuts are shown in the top and bottom line of the figure. The integration ranges from the blue-shifted component are in dark gray and light gray shows the red component. The v_lsr is shown by a dashed gray line. The two plots of the right main panel show position-velocity diagrams for the upper and lower cuts representing the same spectra, respectively. Short arrows indicate the position of velocity jumps seen in the spectra and mark the same positions in the extracted spectra and the position-velocity cuts.