Top panel: Distribution of radio spectral index between 1400 and 150 MHz for CRe injected by shocks, for our fiducial post-processing treatment of CRe spectra, for a 21.25³ Mpc³ volume at z = 0. Bottom panel: Map of the ratio between the synchrotron radio power at 150 MHz For the same volume and epoch, computed assuming a fixed α = −2 for the momentum spectrum of CRe injected by shocks, and the power from CRe assuming their realistic spectrum as in Sect. 2.7.