Left: observed η-PDF of the cloud Orion B. Dashed–dotted black line: log-normal fit of the low-η part of the PDF. Dashed red and green lines: power law with exponent αη = 2, corresponding to an underlying s-PDF with a power-law exponent αs = 3/2, a signature of collapsed regions. Right: observed η-PDF of the cloud Polaris. Dashed–dotted black line: log-normal fit of the low-η part of the PDF. Dashed red and green lines: power laws respectively with exponents αη = 4 and 2, corresponding to an underlying s-PDF transiting from log-normal to power laws with exponents αs = 2 and 3/2, respectively.