FORMATION OF QUASARS AT HIGH-REDSHIFT

Analytic arguments have suggested that the existence of high-redshift quasars challenges hierarchical galaxy formation theories in which the majority of galaxies form late. We address this issue by using a seri es of numerical simulations of the biased cold dark matter model with and without gas dynamics. Potential quasar sites are identified with m assive density peaks collapsing to form massive self-gravitating cold, gas clouds. The Press-Schechter formalism, using a Gaussian filter wi th delta(c) = 1.61, correctly predicts the number of high-mass dark ha loes. Very efficient cooling and angular momentum transfer to the dark halo, however, allow the gas to become much denser than naive predict ions would suggest. We find that there are > 10(3) times the required number of potential quasar sites at z = 4.5; at z = 8 there is already at least one site in our simulation volume of 10(6) Mpc(3). Thus site s for quasars could easily form at significantly higher redshifts than those of observed quasars, even in models where most galaxy formation occurs late.