Cooling timescales of CR electrons in a slice through the center of galaxies with different stellar masses, M_⋆, (top to bottom panels) and different redshifts, z (left to right panels). The value of γ_e used in this plot corresponds to the one at which CR electrons contribute mostly to the synchrotron emission at 1.4 GHz, i.e., at which ν_c = ν_obs = 1.4 GHz; see Eq. (32). The total timescale, τ_e, (solid lines) has contributions from bremsstrahlung (τ_brems, dashed lines), synchrotron losses (τ_synch, dotted lines), inverse Compton losses (τ_IC, dashed-dotted lines), and ionization losses (τ_ion, dashed-dotted-dotted lines). Grey vertical lines indicate the characteristic radius R_gal, i.e., they enclose 2R_gal.