The Impact of Population Iii Objects on the Early Universe

We study the effects of the ionizing and dissociating photons produced by Pop III objects on the surrounding intergalactic medium. We find that the typical size of a H2 photodissociated region is smaller than the mean distance between sources at z ≈ 20−30, but larger than the ionized region. This implies that clearing of intergalactic H2 occurs before reionization of the universe is complete. In the same redshift range, the softUV background in the Lyman-Werner bands, when the intergalactic H and H2 opacity is included, is found to be JLW ≈ 10 −28 − 10 erg cm s Hz. This value is well below the threshold required for the negative feedback of Pop III objects on the subsequent galaxy formation to be effective. We have combined these semi-analytical results with high resolution N-body simulations, to study the topological structure of photoionization and photodissociation and the evolution of the H and H2 filling factor.