Left : model-predicted integrated intensities for a piecewise LN and PL N-PDF, with N₀ = 2 × 10²¹ cm⁻², r_thres=1.5, α = 3 and σ increasing from 0.3 to 0.8. All predicted integrated intensities vary by 10% at most, which illustrates the degeneracy on the parameter σ in the particular case of low N₀ and strong PL component. The right panel displays the corresponding N-PDF with varying σ. The dashed vertical line shows the column density limit below which the emission of all lines is less than 0.1 K km s⁻¹ .