Distributions of (a) FWHM and (b) σ_NT of the p–H₂CO (3_0,3–2_0,2) transition. The blue and red histograms represent the H₂CO Main and H₂CO Sub components, respectively, with the corresponding dashed lines marking their median values. Panel c: relation between σ_NT and L_bol. The black, blue, and red dashed lines indicate the power-law fits for all components combined, the Main components, and the Sub components, respectively.