Upper panel: column density distribution of molecular hydrogen for a prestellar core extracted from the StarFormat database. Black and white contours show 30, 50, 70, and 95 per cent of the H₂ column density peak and of the 850-μm dust emission (Stokes I) peak, respectively. The scale bar to the right gives N(H₂) in logarithmic scale. Lower panel: polarisation map for the core depicted in the upper panel (r_model = 2.8 × 10⁴ AU). The scale bar to the right gives I_p in Jy/( beam) and it refers to the coloured map which has been debiased for values below 3σ. Magenta contours show 30, 50, 70, and 95 per cent of the 850-μm dust emission (Stokes I) peak; white vectors show the direction of the magnetic field. The synthesised beam is shown in the lower left corner.