Gas kinetic temperature derived from para-H₂CO (3–2) (blue points) and NH₃ (2, 2)/(1, 1) (black points) ratios along the northern 10 km s^-1 filament of the OMC-1 ridge (distance from IRc2, α = 05:35:14.48, δ = –05:22:30.56, J2000). The blue and black lines are the fitted results for para-H₂CO and NH₃, respectively, with distance R > 0.5′. The red and green lines are the expected relationships from a Stefan-Boltzmann law and modified Stefan-Boltzmann law (see Sect. 4.5), respectively, assuming Orion KL is the dominant source with an approximate luminosity of 10⁵ L_⊙ (Downes et al. 1981; Wiseman & Ho 1998).