Secondary correlations. Each panel in this figure shows the metallicity – IMF slope plane, color-coded by a different quantity derived from our stellar population analysis. White dashed lines indicate the shape of the iso-contours. The color-coding of the top panels corresponds to the age (left) and the stellar surface density (right) of each Voronoi bin within our sample of F3D galaxies. No noticeable correlation is found between these two quantities and the scatter in the metallicity-IMF slope plane. However, both the [Mg/Fe], and particularly the effective star formation rate surface density, seem to correlate with the scatter in IMF slope values in the low metallicity ([M/H] ≲ −0.1) regime. This may indicate a secondary dependence of IMF variations on star formation rate-related quantities, on top of the main trend with metallicity shown in Fig. 4.