Downsizing of supermassive black holes from the SDSS quasar survey (II).
  Extension to z~4
  Starting from the quasar sample of the Sloan Digital Sky Survey (SDSS) for
which the CIV line is observed, we use an analysis scheme to derive the
z-dependence of the maximum mass of active black holes, which overcomes the
problems related to the Malmquist bias. The same procedure is applied to the
low redshift sample of SDSS quasars for which Hbeta measurements are available.
Combining with the results from the previously studied MgII sample, we find
that the maximum mass of the quasar population increases as (1+z)^(1.64+/-0.04)
in the redshift range 0.1<z<4, which includes the epoch of maximum quasar
activity.
