Lyα SB of recombination (panel a) and collisional excitation (panel b) processes in a simulation snapshot at z = 4.8, for the gas at densities below half the critical self-shielding density in a narrowband with Δλ_obs = 8.75 Å, or ∼2.7 h⁻¹ cMpc; the projections are made with pixel grid sizes of 1024 × 1024. These images show the entire (two-dimensional) spatial extent of the simulation, 40 × 40 h⁻² cMpc² (25.8 × 25.8 arcmin²). Panels c and d: same maps, but without a density cut-off.