Cosmological H II regions and the photoionization of the intergalactic medium

The classical H II region problem is generalized to treat the case of a point ionizing-radiation source in a gas expanding cosmologically in a Friedmann-Robertson-Walker universe, applying a cosmological generalization of the static Stromgren radius to obtain the time dependence of the radius and peculiar velocity of the source ionization front. Numerical results are presented graphically and characterized in detail. It is shown that the number and luminosity of the observed high-redshift quasars is insufficient to photoionize enough of the low-density intergalactic medium to satisfy the Gunn-Peterson test for neutral H atoms at z greater than 3.5. 18 references.