On the cosmological evolution of the black hole - host galaxy relation
  in quasars
  Quasars are useful tracers of the cosmological evolution of the black hole
mass - galaxy relation. We compare the expectations of Semi-Analytical Models
(SAM) of galaxy evolution, to the largest available datasets of quasar host
galaxies out to z=3.
  Observed quasar hosts are consistent with no evolution from the local M(BH) -
L(host) relation, and suggest a significant increase of the mass ratio Gamma =
M(BH)/M(host) from z=0 to z=3. Taken at face value, this is totally at odds
with the predictions of SAM, where the intrinsic Gamma shows little evolution
and quasar host galaxies at high redshift are systematically overluminous
(and/or have undermassive BH). However, since quasars preferentially trace very
massive black holes (10^9-10^10 Msun) at the steep end of the luminosity and
mass function, the ensuing selection biases can reconcile the present SAM with
the observations. A proper interpretation of quasar host data thus requires the
global approach of SAM so as to account for statistical biases.
