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 1010 M☉ 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 1013 M☉ and σ* 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 the MBH-Mbulge-σ* correlations observed in the local universe do not reflect the relation between those quantities at the epoch of galaxy formation.