N-PDFs of the gas traced by H I (left panel) emission, HISA (middle panel), and ¹³CO (right panel) in units of hydrogen atoms per square cm. The light green lines show the log-normal fit in each panel. σ is the width of the log-normal distribution. The dashed vertical lines in each panel mark the column density threshold, and the solid vertical lines mark the mean column densities. The red line in the ¹³CO panel shows the power-law fit with an index − α to the high column density tail.