Spectral indices along the tails of NGC 1265 and IC 310. The flux densities are measured in circular regions with radii of 1.8′and 1′at equal spacings of 100 kpc and 60 kpc for NGC 1265 and IC 310, respectively. These regions are marked with circles in the cutout images presented in Figs. D.1 and D.2. The error bars indicate the spectral index uncertainty when taking only the r.m.s. map noise into account (relevant for comparing the evolution of the spectral index along a spatial dimension), while the shaded regions include the 10% flux density uncertainty (relevant for comparing the spectral index between different frequencies).