Lyα-driven outflows around star-forming galaxies

We present accurate Monte Carlo calculations of Ly alpha radiation pressure in a range of models which represent galaxies during various epochs of our Universe. We show that the radiation force that Ly alpha photons exert on hydrogen gas in the neutral intergalactic medium (IGM), that surrounds minihaloes that host the first stars, may exceed gravity by orders of magnitude and drive supersonic winds. Ly alpha radiation pressure may also dominate over gravity in the neutral IGM that surrounds the H II regions produced by the first galaxies. However, the radiation force is likely too weak to result in supersonic outflows in this case. Furthermore, we show that Lya radiation pressure may drive outflows in the interstellar medium of star-forming galaxies that reach hundreds of kilometres per second. This mechanism could also operate at lower redshifts z less than or similar to 6, and may have already been indirectly detected in the spectral line shape of observed Ly alpha emission lines.