  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).

Cosmology and Nongalactic Astrophysics