Combined radio-SFR plots. Panels a and b show the radio Σ_SFR at 144 and 1365 MHz, respectively, as function of the hybrid Σ_SFR. Data points are colour-coded, so that young CREs are shown in red, middle-aged CREs are shown in green, and old CREs are shown in blue. Panels c and d show the relation only for young CREs, where the various galaxies are now colour-coded. Solid lines show in blue the 1:1 Condon’s relation and in orange the best-fitting power-law relations with 3σ confidence intervals indicated by dashed lines. Details of the best-fitting relations can found in Table 2.