Comparison between our fiducial model (shaded regions) and two other models with different optical depths: an optically thin case (T_S = 8000 K, dot-dashed lines) and a more optically thick one (T_S = 80 K, dashed lines). From top to bottom: rotation velocity, velocity dispersion, midplane density, scale height and surface density as a function of R. Only the averaged profiles are shown, smoothed at the spatial resolution of 0.2 kpc. Different regimes predict significantly different column densities.