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We propose a new evolutionary model for the optical luminosity function of quasars. Our analytical model is derived from fits to the empirical luminosity function estimated by Hartwick & Schade and Warren, Hewett, & Osmer on the basis of more than 1200 quasars over the range of redshifts 0 4. 5 implies that quasars may have started their cosmic fireworks at zf_ ~ 5. 2-5. 5. Forthcoming surveys of quasars at these redshifts will be critical to constrain the epoch of quasar formation. All the results we derived here are based on observed quasars and are therefore subject to the bias of obscuration by dust in damped Lyα systems. Future surveys of these absorption systems at z ~> 3 will also be important if the formation epoch of quasars is to be known unambiguously.
Yichuan C. Pei (Sun,) studied this question.