Column density PDFs of the IRDCs in the sample. The PDFs are normalized so that a linear fit to the range lnA_V = 2−3 fulfills the boundary condition p(lnA_V = 2.0) = 1. The dashed histogram shows the PDF of the Ophiuchus cloud from K09. The black dotted vertical line marks the upper limit of the K09 data (A_V = 25 mag). The black dotted curve shows, for reference, a log-normal function with μ = 1.2, σ_lnN = 0.9 (not a fit). The colored vertical dotted lines show the saturation limits of the IRDCs.