Left: total gas column density towards the NGC 1333 central clump. Contours similar to Fig. 2. The solid triangles indicate the position of the different dense cores identified by Rosolowsky et al. (2008). Centre: N₂H⁺ (1–0) integrated emission map obtained with the IRAM 30 m telescope. Right: NH₃ (1, 1) integrated emission map obtained with the Effelsberg 100 m telescope. Offsets are referred to the map centre with coordinates in radio projection. Contours are equally spaced every 1.2 K km s^-1 and 1.0 K km s^-1 in the N₂H⁺ and NH₃ maps, respectively. In each case, the area surveyed by our molecular observations is enclosed by a dashed line. The area mapped in N₂H⁺ is also delineated by a white dashed line on the left panel. The different FWHM are indicated at the lower left corner in the corresponding plots.