Illuminated edge of the Horsehead in the H₂ line at 2.12 µm derived from the F212N and F210M filters (red), in the F335M (green) filter, and F187N (red) filter (top). Profiles of the relative brightness after background correction (normalized at a distance of 2″ from the edge) along the four cuts in the H₂ line at 2.12 µm (smoothed with a window size of 5 pixels, corresponding to ~0.3″, in order to limit the noise), in the F335M filter and in the F187N filter (bottom). The three individual images are shown in logarithmic scales. They are used to make the RGB composite map. The four solid lines show the four cuts we use, labeled 1 to 4 from left to right. The position ɀ = 0″ in the profiles coincides with the more external edge of the PDR, as traced by the F335M filter (see Sect. 5.1). Negative values of ɀ are towards the illuminating star.