Tracks showing the evolution of the radio and NIR luminosity of a 3C 48-like model with redshift. The redshift data points are given from right to left, starting with 3C 48’s (and the other two comparative sources, Mrk 231 and Arp 220) intrinsic redshift (bold open square). The first thin open square from right indicates a redshift of z = 1, the next thin open square is equal to z = 2, and so on to z = 7. The vertical solid line indicates the IFRS NIR flux cutoff-criterion S_{3.6   μm}    <    30   μJy, the other solid line represents S_20   cm/S_{3.6   μm}    =    500.