Influence of the magnetic field on the PDR lines. Top: model predictions of the [C ii] and [O i] intensities (I_model) normalised by their observed value (I_obs) as a function of magnetic strength B_mag. The effective density in the PDR is indicated for each B_mag value. Bottom: fraction of [C ii] coming from the PDR, scaled to the [O i] 145 μm prediction, assuming that all of it originates in the PDR. Models in the shaded area are not valid with respect to the upper limit on the H i column density. (This figure is available in color in electronic form.)