Left panel: dust effective temperature (T_eff) as a function of the total column density (N(H₂); in logarithmic scale) for all the points belonging to the NGC 1333 clump presented in Fig. 2 (grey squares). Positions with angular distances R ≤ 200′′ from the centre of the optical nebula or R ≤ 50′′ from the IRAS 1–8 sources are displayed with open symbols. Positions presenting an I(N₂H⁺) ≥ 1.2 K km s^-1 are highlighted in red. The blue dashed line indicates the eye-fitted lower envelope of all the points in the cloud. The estimated dust effective temperature (T_eff = 12 K) floor is indicated by a dotted line. Right panel: normalized histograms of the dust effective temperature for the NGC 1333 region (grey) compared with only those points having significant N₂H⁺ emission (red).