Space density evolution of quasars

It is stated that attempts to obtain interesting cosmological information from the study of quasars have been thwarted by the apparent large spread in quasar luminosities, so that the conventional Hubble plot produces a scatter diagram. Several authors have used an absolute magnitude-redshift diagram to provide an improved Hubble diagram. However, little work has been done on using the (M.log z) plot as a cosmological indicator in its own right, in place of the Hubble diagram. It is shown here that although evolution may be zero, the uncertainty in the quasar luminosity function allows an upper limit on the quasar space density. (author)