Left: averaged (see Sect. 3.2) velocity-integrated intensity ratio map of para-H₂CO 0.5 × [(3₂₂–2₂₁ + 3₂₁–2₂₀)/3₀₃–2₀₂] in the OMC-1. Middle: kinetic temperatures derived from the para-H₂CO (3–2) line ratios. Right: kinetic temperatures derived from NH₃ (2, 2)/(1, 1) ratios observed with the GBT (beam size ~30′′; Friesen et al. 2017). Black contours show the contour of integrated intensity of para-H₂CO 3₀₃–2₀₂ at 1.9 K km s^-1 (see Fig. 2). Red contours show the velocity-integrated intensity (V_LSR = –30 to +30 km s^-1) of the H41α recombination line observed with IRAM (beam size ~30′′; Goicoechea et al. 2015). Stars show the locations of the Trapezium stars (θ¹ Ori A, B, C, D, and E). The unit of the color bars of the middle and right panels is in both cases Kelvin.