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 hole (BH) masses for a large number of quasars in three samples. The largest black hole masses exceed 10(10) M-circle dot and are found to occur in the objects with the highest luminosities. Such BH masses, when converted to galaxy bulge mass and luminosity, indicate masses in excess of 10(13) M-circle dot and sigma in excess of 700 km s(-1). Such massive galaxies have never been observed. The largest BHs reside, almost exclusively, in high-redshift quasars. All this is inconsistent with several suggested scenarios of BH and galaxy formation. Possible ways out are that either the observed size-luminosity relationship in low-luminosity AGNs does not extend to very high luminosity or else M-BH-M-bulge-sigma(*) the correlations observed in the local universe do not reflect the relation between those quantities at the epoch of galaxy formation.