The impact of population 3 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 H_2 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 the intergalactic H_2 occurs before reionization of the universe is complete. In the same redshift range, the soft-UV background in the Lyman- Werner bands, when the intergalactic H and H_2 opacity is included, is found to be J_LW = 10^-28 - 10^-26 erg cm^-2 s^-1 Hz^-1. This value is well below the treshold 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 H_2 filling factor