Absorption spectra of C IV generated with light rays passing through the centre (upper panels), at 5 pc from the centre (middle panels), and at 15 pc from the centre (bottom panels), all along the z-axis. In this figure, we display the absorption profiles produced with R32-AL on the left and R32-TR on the right. In the same panel, different lines have different spectral resolution: 1 km s⁻¹ (solid), 10 km s⁻¹ (dashed) and 30 km s⁻¹ (dotted).