Local Radiative Feedback in the Formation of the First Protogalaxies

The formation of the first galaxies is strongly affected by the radiative feedback from the first generations of stars. This feedback is manisfested by the heating and ionization of the gas which lies within the H II regions surrounding the first stars, as well as by the photodissociation of hydrogen molecules within the larger Lyman-Werner (LW) bubbles that surround these sources. Using a ray-tracing method in three-dimensional cosmological simulations, we self-consistently track the formation of, and radiative feedback from, individual stars in the course of the formation of a protogalaxy. We compute in detail the H II regions of each of these sources, as well as the regions affected by their molecule-dissociating radiation. We follow the thermal, chemical, and dynamical evolution of the primordial gas, as it becomes incorporated into the protogalaxy. While the IGM is, in general, optically thin to LW photons over ~ 100 kpc, the high molecule fraction that is built up in relic H II regions and their increasing volume-filling fraction renders the local IGM optically thick to LW photons over much smaller scales. We find that efficient accretion onto Population III relic black holes may occur after ~ 60 Myr from the time of their formation, by which time the photo-heated relic H II region gas can cool and re-collapse into the 10⁶ Mₛolar minihalo which hosts the black hole. Also, Pop II. 5 stars, postulated to have masses of the order of 10 Mₛolar, may form from this re-collapsing relic H II region gas, but their formation can be easily suppressed by LW feedback from neighboring star-forming regions. Overall, we find that the local radiative feedback from the first generations of stars suppresses the star formation rate by only a factor of, at most, a few.