Brightness temperature versus AGN fraction. Left: AGN fraction derived from the CyE95 fit. Right: AGN fraction derived from the CiS12 fit. The solid, dashed, and dotted blue lines indicate the maximum brightness temperature from starbursts for a synchrotron spectral index α of −0.7, −0.8, and −0.9, respectively, as per Condon et al. (1991). Points above these lines cannot be driven by pure star formation. Estimates with f_AGN < 0.01 were offset by 0.01 for visual clarity. Points are coloured by the classification of Best et al. (in prep.).