Comparison of different T_K estimates along the ISF: (a) T_K(HCN/HNC) (this work), (b) ammonia-derived gas kinetic temperatures T_K(NH₃) (Friesen et al. 2017), (c) Herschel dust temperatures T_dust (Lombardi et al. 2014), and (d) ¹²CO (1–0) excitation temperatures (Nakamura et al. 2012; Shimajiri et al. 2014), all represented with the same colour scale. We note that both dust temperature and column density are underestimated towards the OMC-1 and BN/KL regions as a result of saturation effects and the lack of proper SED fits in the Herschel maps provided by Lombardi et al. (2014). We also note the rapid decrease in T_ex (CO) at the northern end in our maps, which is likely due to subthermal excitation of the ¹²CO (i.e., ) lines at the low densities expected in this region. To facilitate the comparison of these figure, we indicate the intensity contour withI(N₂H⁺) = 1.5 K km s⁻¹ in panels b–d. Circles and stars are similar to Fig. 1.