Radiation-hydrodynamical collapse of pre-galactic clouds in the ultraviolet background

To explain the effects of the ultraviolet (UV) background radiation on the collapse of pre-galactic clouds, we implement a radiation-hydrodynamical ca lculation, combining one-dimensional spherical hydrodynamics with an accura te treatment of the radiative transfer of ionizing photons. Both absorption and scattering of UV photons are explicitly taken into account. It turns o ut that a gas cloud contracting within the dark matter potential does not s ettle into hydrostatic equilibrium, but undergoes run-away collapse even un der the presence of the external UV field. The cloud centre is shown to bec ome self-shielded against ionizing photons by radiative transfer effects be fore shrinking to the rotation barrier. Based on our simulation results, we further discuss the possibility of H-2 cooling and subsequent star formati on in a run-away collapsing core. The present results are closely relevant to the survival of subgalactic Population III objects as well as to metal i njection into intergalactic space.