Dense gas kinematics in the NGC 1333 proto-cluster traced by our IRAM 30 m N₂H⁺ observations. Central panel: N₂H⁺ integrated emission. The red squares enclose those subregions fitted with two independent components (see text), typically found surrounding the most prominent emission clumps detected in this molecule. Lateral subpanels: representative N₂H⁺ (JF₁F = 101–012) spectra (isolated component) within selected regions (spectra 1–8). The position of the spectra are indicated in the upper-left corner of each subpanel. We note the presence of two clearly separated components detected in N₂H⁺ in spectra 2–5. Although still fitted with two components, a third line superposition is suggested by the shape of the line profile in spectrum 7.