Ridge plots showing PDFs of integrated ¹³CO emission (left panel) and H₂ surface density values inferred from dust emission (right panel). For the left panel, each row shows the PDF of the W_CO values of all spectra fitted with N_comp components (indicated with the number to the left and the colour-shading of the PDF). For the right panel, each row shows the PDF of the values associated with ¹³CO spectra fitted with N_comp components (indicated with the number to the left and the colour-shading of the PDF). For better visibility, three of the PDFs have been scaled in size, which is indicated next to the PDFs. The values to the right of the PDFs indicate the first quartile (Q₁), the median (Q₂), and the third quartile (Q₃) of the distribution.