CDM HR column density maps and [C II] surface-brightness. Top row: Column density maps at z = 12 and z = 6 obtained by projecting a slice passing through the centre of the CDM HR simulation box along a width equal to one-tenth of the box side (10 cMpc/h) and discretising it on a grid of 512 × 512 pixels. This results in a pixel linear size of about 19.5 ckpc/h. Bottom row: [C II] surface-brightness maps at z = 12 and z = 6 obtained by projecting the [C II] emission from the same slice passing through the centre of the CDM HR simulation box.