Lyα SB resulting from the combination of recombination emission (of all gas in the simulation) below the mirror limit and collisional excitation of gas below half the critical self-shielding density, covering an area of 20 × 20 arcmin², or 31.0 × 31.0 h⁻² cMpc², in a narrowband with Δλ_obs = 8.75 Å (corresponding to ∼2.7 h⁻¹ cMpc) in a simulation snapshot at z = 4.8. The images are made by the projection method (Sect. 2.4.1) onto a pixel grid of 6000 × 6000; this is the same pixel size as MUSE, making this image the equivalent of a mosaic of 20 × 20 MUSE pointings (more details on MUSE follow in Sect. 3.3). Regions 1 and 2, indicated by the white rectangles, will be studied in more detail later. Also shown in the bottom left corner are the scales of the MUSE FOV (1 × 1 arcmin²) and 1 h⁻¹ cMpc.