Do all QSOs have the same black hole mass?
  QSOs from SDSS, 2QZ and 2SLAQ covering an order of magnitude in luminosity at fixed redshift exhibit similar amplitudes of clustering. In addition, QSO clustering evolution at z>0.5 is well fitted by a model that assumes a fixed host halo mass, implying that QSOs may occur in a relatively narrow range of halo and BH mass. We argue that the slow evolution of early-type galaxies out to z~1-2 may also provide support for a slow evolution of QSO host BH masses. The result would mean that if high-z QSOs radiate at Eddington rates then low-z SyI must radiate at ~100x less than Eddington. We conclude that models where QSOs radiate at L_Edd require M_BH and M_halo to be decoupled to circumvent the clustering results. While single BH mass and flickering models fit the z>0.5 clustering results, they appear to be rejected by the z~0, M_BH-L relation from reverberation mapping. We find that the inclusion of z<0.5 QSO clustering data improves the fit of a long-lived QSO model and suggest that the predictions of a PLE model for QSO BH masses agree reasonably with UV-bump and reverberation estimates (abridged). 
T. Shanks, S.M. Croom, S. Fine, N.P. Ross and U. Sawangwit
astro-ph.CO