The largest black holes and the most luminous galaxies
  The empirical relationship between the broad line region size and the source luminosity in active galactic nuclei (AGNs) is used to obtain black holes (BH) masses for a large number of quasars in three samples. The largests BH masses found exceed 10^{10} Msun and are correlated, almost linearly, with the source luminosity. Such BH masses, when converted to galactic bulge mass and luminosity, indicate masses in excess of 10^{13} Msun and sigma(*) in excess of 700 km/sec. Such massive galaxies have never been observed. The largest BHs reside, almost exclusively, in high redshift quasars. This, and the deduced BH masses, suggest that several scenarios of BH and galaxy formation are inconsistent with the observations. Either the observed size-L relationship in low luminosity AGNs does not extend to very high luminosity or else the M(BH)-M_B(bulge)-sigma(*) correlations observed in the local universe do not reflect the relations of those quantities at the epoch of galaxy formation. 
Hagai Netzer (Tel Aviv University)