Electromagnetic properties of MBHBs and their host galaxies for MBHBs contributing 90% of the background. The left panels show B, V, and K magnitudes; the right panels radio flux at 2 GHz, X-ray flux at [2-10] keV and bolometric luminosity, where the horizontal line marks L_bol = 10⁴⁵ erg s⁻¹, as a typical value for quasar luminosities. Sources with magnitude fainter than 34 are set at 34, and similarly sources with X-ray flux < 10⁻¹⁹ and radio flux < 10⁻³ μJy are set at these values for clarity. For MBHs with f_Edd < 10⁻³ we show an upper limit to the brightness ignoring the correction to radiative efficiency (filled squares) and a lower limit including the correction (empty squares connected to the filled squares).