Mass fraction of the small dust grains (VSAC and SAC) as a function of the mean insterstellar radiation field ⟨U⟩. The cyan and red points are measurements for the individual pixels (along with their uncertainties) for the disk and the halo, respectively (with a crude separation at |z| = 2 kpc). The purple symbols are median values and uncertainties within circular apertures with a radius of 0.8 kpc centered at the regions from A to F. The gray square in this plot shows the median value (and the respective uncertainty) of the dust emission feature located at ∼4 kpc above the center of the galaxy (see Fig. 4) within an elliptical aperture encompassing the feature.