Left: Spitzer 8 μm image of SDC13 in grey scale on top of which we marked the 31 single-pointing positions we observed in N₂H⁺(1–0), and the skeletons of each filament (thick solid lines). The size of the black circles represents the 30 m beam size at 3.2 mm. Right: examples of three N₂H⁺(1–0) spectra (displayed on temperature scale) observed at three different positions (1, 10, and 24). Their corresponding hyperfine structure fits are displayed as yellow solid lines. The remaining spectra are displayed in Fig. 3. The vertical dashed line corresponds to the systemic velocity of the cloud (i.e. V_sys = 37.0 km s^-1) as measured from the isolated component of the hyperfine structure.