Effect of Cosmic Ultraviolet Background on Star Formation in High-redshift Galaxies

The effect of the cosmic UV background on star formation in high-redshift galaxies is explored by means of high-resolution cosmological simulations. The simulations include star formation, three-dimensional radiative transfer, and a highly detailed interstellar medium model, and reach spatial resolution sufficient to resolve formation sites for molecular clouds. In the simulations, the local radiation field in the Lyman-Werner band around star-forming molecular clouds dominates over the cosmic UV background by a factor of 100, similarly to the interstellar radiation field in the Milky Way and in a few high-redshift galaxies for which measurements exist. The cosmic UV background in the Lyman-Werner band, therefore, is essentially irrelevant for star formation in normal galaxies.