The estimation of black-hole masses in distant radio galaxies
  We have estimated the masses of the central supermassive black holes of 2442 radio galaxies froma catalog compiled using data from the NED, SDSS, and CATS databases. Mass estimates based on optical photometry and radio data are compared. Relationships between the mass of the central black hole $M_p^{bh}$ and the redshift $z_p$ are constructed for both wavelength ranges. The distribution of the galaxies in these diagrams and systematic effects influencing estimation of the black-hole parameters are discussed. Upperenvelope cubic regression fits are obtained using the maximum estimates of the black-hole masses. The optical and radio upper envelopes show similar behavior, and have very similar peaks in position, $z_p \simeq 1.9$, and amplitude, $\log M_p^{bh}$ = 9.4. This is consistent with a model in which the growth of the supermassive black holes is self-regulating, with this redshift corresponding to the epoch when the accretion-flow phase begins to end and the nuclear activity falls off. 
M.L. Khabibullina, O.V. Verkhodanov
astro-ph.CO