The radiative feedback of the first cosmological objects

hierarchical models of structure formation, an early cosmic UV background ( UVB) is produced by the small (T-vir less than or similar to 10(4) K) halos that collapse before reionization. The UVB at energies below 13.6 eV suppr esses the formation of stars or black holes inside small halos by photodiss ociating their only cooling agent, molecular H-2. We self-consistently comp ute the buildup of the early UVB in Press-Schechter models, coupled with H- 2 photodissociation both in the intergalactic medium (IGM) and inside viria lized halos. We find that the intergalactic H-2 has a negligible effect on the UVB, both because its initial optical depth is small (less than or simi lar to 0.1) and because it is photodissociated at an early stage. If the UV sources in the first collapsed halos are stars, then their UV flux suppres ses further star formation inside small halos. This results in a pause in t he buildup of the UVB, and reionization is delayed until larger halos (T-vi r greater than or similar to 10(4) K) collapse. If the small halos host min iquasars with hard spectra extending to similar to 1 keV, then their X-rays balance the effects of the WE, the negative feedback does not occur, and r eionization could be caused by the small halos.