Fraction of thermal radio continuum emission in NGC 891 and 4565 at 1.5 and 6 GHz. The angular resolution in all panels is 12″. Each map is overlaid with contours of the total radio emission at the respective frequency, identical to those shown in shown in Figs. 3a and b and Figs. 4a and b, respectively. Contour levels are σ × (3, 6, 12, 24, etc) of the corresponding total emission maps (see Tables 2 and 3). Filled black circles indicate the size of the synthesised beam.