Temperature (in Kelvin) as function of line ratio of the H₂CO transitions with J_up = 4. The datapoints show the calculated excitation temperatures from the individual pixels of the maps shown in Fig. 6. Square markers in the upper left side of the figure correspond to the ortho-H₂CO transitions, while circle markers in the lower right side correspond to the para-H₂CO transitions. The solid color lines indicate the RADEX models of kinetic temperature as function of line ratio for different values of H₂ volume density as indicated in the lower right panel. These models were computed using H₂CO column densities of (a) 3.8 × 10¹⁴cm⁻² and (b) 5.2 × 10¹³cm⁻², which correspond to the column densities at A/B and the average on the other positions, respectively.