Scenario (2) – compression model. The effect of increasing the initial 10 μG magnetic field on the radio excess and synchrotron spectrum (blue continuous line). Diamond symbols mark the fractional increase of the magnetic field in increments of 0.25, integer values are highlighted. The orange dashed line shows the same model when including ionization and Bremsstrahlung losses. The green dotted line shows the same model when also increasing the gas density as n_gas ∝ B^3/2.