Example of RADEX non-LTE modelling of the N(H₂CO)–n(H₂) relation for AGAL008.684−00.367 at a kinetic temperature of 55 K (see Sect. 3.4). Black dashed and solid lines are para-H₂ CO 4₀₄–3₀₃ integrated intensities and para-H₂CO 4₀₄–3₀₃/3₀₃–2₀₂ integrated intensity ratios, respectively. Tothe measured parameters, para-H₂ CO 4₀₄–3₀₃ integrated intensity (orange solid and dashed lines represent observed value and uncertainty) and para-H₂ CO 4₀₄–3₀₃/3₀₃–2₀₂ integrated intensity ratio (white solid and dashed lines) are corrected by the relevant beam-filling factors (see Table A.6). The colour map shows the optical depth of the para-H₂ CO 3₀₃–2₀₂ line. The purple line in the upper green area corresponds to optical depth τ(para-H₂CO 3₀₃–2₀₂) = 1.0.