Left panel: NIR VISTA image of M42 in the K_S band dominated by interstellar emission from vibrationally excited H₂. The intensity scale is chosen to enhance the very bright NIR emission from gas illuminated by the strong FUV field from the Trapezium stars; and locally by thermally excited shocked gas in outflows (Fig. B.6 shows a larger image that enhances the much more extended NIR emission). Black contours show the CH⁺ J = 1–0 intensities from 1 to 46 K km s⁻¹ in steps of 5 K km s⁻¹. Right panel: FUV radiation field, G₀, estimated from FIR luminosities (Goicoechea et al. 2015a). The gray area around BN/KL indicates positions where the Herschel photometric data is saturated.