Density plots of the dust heating fraction from unevolved stellar populations F_unev. vs. a number of physical parameters, obtained from HELGA IV. A red colour indicates a small number of data points in that area of the plot, yellow at a large number. Kendall’s correlation coefficient τ is given in each panel. First row: dust mass, stellar mass, dust-to-stellar mass ratio. Second row: star formation rate, specific SFR, temperature of the cold dust in the ISM. The black line is a best fit linear model, the green line is the relation found by De Looze et al. (2014) for M 51. Parameters are derived according to the MAGPHYS SED model.