Comparison of gas kinetic temperatures derived from para-H₂CO 3₂₁–2₂₀/3₀₃–2₀₂ against the Herschel 250 μm flux. The straight line is the result from a linear fit for the five sources with all 218 GHz para-H₂CO lines detected. N159S provides with respect to T_kin a 3σ upper limit. Thus this point may be located much farther to the left, closer to the linear fit obtained from the other five sources.