Suppression of H2-cooling in protogalaxies aided by trapped Lyα cooling radiation

英文摘要：

We study the thermal evolution of UV-irradiated atomic cooling haloes using high-resolution three-dimensional hydrodynamic simulations. We consider the effect of H^- photodetachment by Lyα cooling radiation trapped in the optically-thick cores of three such haloes, a process which has not been included in previous simulations. H^- is a precursor of molecular hydrogen, and therefore, its destruction can diminish the H2 abundance and cooling. Using a simple high-end estimate for the trapped Lyα energy density, we find that H^- photodetachment by Lyα decreases the critical UV flux for suppressing H2-cooling by up to a factor of \approx 5. With a more conservative estimate of the Lyα energy density, we find the critical flux is decreased only by ~15-50 percent. Our results suggest that Lyα radiation may have an important effect on the thermal evolution of UV-irradiated haloes, and therefore on the potential for massive black hole formation.