Absorption spectra at t/t_cc = 1.7 of ions tracing the cold phase of the gas generated with light rays passing through the centre (in blue), 5 pc from the centre along the x- (dashed orange line) and z-axis (solid orange line), and 15 pc from the centre along the x- (dashed green line) and z-axis (solid green line). In this figure, we display in the upper left panel the absorption profiles of the C II in the simulation R32-AL, in the upper right panel the C II in R32-TR, while the lower panels show the lines of the Si II in the simulation R32-AL (left) and R32-TR (right). We show that C II and Si II are tracers of the denser part of the cloud. These ions produce deeper absorption lines in the presence of a transverse magnetic field (see also Fig. C.1 for t/t_cc = 1.2). At t/t_cc = 1.7, the differences are evident along the lines of sight observing the cloud centre and at 15 pc from the centre in the direction of the magnetic field, while at t/t_cc = 1.2 the differences can be seen along the cloud centre and at 5 pc from it.