Correlation between the 24 μm integrated intensity and: the mass of dense gas (left) and the mass of gas in the PL part of the N-PDF (right) for pixels within our M51 test region. Each data point corresponds to a pixel within our field. The symbol size and grey shading represent f_PL, the mass fraction of the gas in the PL part of the N-PDF. Symbols with a red outline identify pixels where f_PL ≥ 25% and the slope of the PL α ∈ [2.5,5]. The dotted line is a linear fit to the pixels where f_PL < 5%. The thick red line is a fit to the points where f_PL ≥ 25% and α ∈ [2.5,5]. The latter fit has a correlation coefficient r = 0.85 and slope s = 1.0.