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