Maximum cosmic redshift of quasars at Z > 3

Timing arguments and current theories of galaxy evolution are used to calculate the maximum cosmological redshift Z_max below which quasars first formed in the nuclei of galaxies. On the assumption that the mass density of the universe is dominated by massive neutrinos ∼ 10 eV of density $$\Omega_\nu \sim 1$$ (Einstein–de Sitter cosmology), it is found that galaxies first formed at redshift $$Z_\text f \sim 10$$, whereas luminous (∼ 10⁴⁸ erg s⁻¹) quasars formed first in cD galaxies at $$Z \lesssim Z_\text {max} \sim 5$$. For a dust-free universe, the space density of high-redshift quasars would show a real decrease at redshifts Z > 4.7.