Numerical simulations of high-redshift star formation in dwarf galaxies

We present first results from three-dimensional hydrodynamic simulations of the high-redshift formation of dwarf galaxies. The simulations use an Eulerian adaptive mesh refinement technique to follow the nonequilibrium chemistry of hydrogen and helium with cosmological initial conditions drawn from a popular Lambda-dominated, cold dark matter (CDM) model. We include the effects of reionization using a uniform radiation field, a phenomenological description of the effect of star formation, and, in a separate simulation, the effects of stellar feedback. The results highlight the effects of stellar feedback and photoionization on the baryon content and star formation of galaxies with virial temperatures of approximately 10(4) K. Dwarf-sized dark matter halos that assemble prior to reionization are able to form stars. Most halos of similar mass that assemble after reionization do not form stars by redshift 3. Dwarf galaxies that form stars show large variations in their gas content because of stellar feedback and photoionization effects. Baryon-to-dark matter mass ratios are found to lie below the cosmic mean as a result of stellar feedback. The supposed substructure problem of CDM is critically assessed on the basis of these results. The star formation histories modulated by radiative and stellar feedbacks are discussed. In addition, metallicities of individual objects are shown to be naturally correlated with their mass-to-light ratios, as is also evident in the properties of local dwarf galaxies.