Sources with orbit period modulation Ib: mass–redshift distribution: contours of the mass–redshift distribution (solid black) of all binary black hole outflows with F/ > =0.5 mJy (thick black curve) and observed periods P _obs between 1 year and 1 minute. This scaled flux limit corresponds to the fiducial VAST survey sensitivity ( F = 0.5 mJy) for the most optimistic conversion of outflow to radio power ( = 1). Contours are shown at 1/4, 1/2, and 3/4 of the maximum value ( dN/ dlog  Mdz 0.06). The distribution shown is smoothed, built by convolving a Gaussian kernel with the underlying merger tree, with smoothing lengths Δlog  M 0.3 in mass and (Δ z = 0.3) in redshift. Also shown are contours of the largest possible (Eddington-limited) flux at a given redshift: F/ = L _edd/4π d ² _L ν for 10 ⁻³, 10 ⁻², ...,  10 ³ Jy (dotted blue, bottom to top). Finally, the thick dotted black line is an empirical relation for the maximum SMBH binary mass vs. redshift (Equation (10)).