2008ApJ...685...21R

In two previous papers, we presented simulations of the first galaxies in a representative volume of the universe. The simulations are unique because we model feedback-regulated galaxy formation, using time-dependent, spatially inhomogeneous radiative transfer coupled to hydrodynamics. Here we study the properties of simulated primordial dwarf galaxies with masses ≲2x10⁸ M_☉ and investigate their impact on the intergalactic medium. While many primordial galaxies are dark, about 100-500 per comoving Mpc³ are luminous but relatively faint. They form preferentially in chain structures and have low surface brightness stellar spheroids extending to 20% of the virial radius. Their interstellar medium has mean density n_H~10-100/cm3, metallicity Z∼0.01-0.1 Z_☉, and can sustain a multiphase structure. With large scatter, the mean efficiency of star formation scales with halo mass, <f_*>∝M²_DM, independent of redshift. Because of feedback, halos smaller than a critical mass, M_crit(z), are devoid of most of their baryons. More interestingly, we find that dark halos have always a smaller M_crit(z) than luminous ones. Metal enrichment of the intergalactic medium is inhomogeneous, with only a 1%-10% volume filling factor of enriched gas with [Z/H]>-3.0 and 10%-50% with [Z/H]>-5.0. At z~10, the fraction of stars with metallicity Z<10^–3 Z_☉ is 10^–6 of the total stellar mass. However, this study focuses on the effects of radiative feedback: mechanical feedback from SN explosions is only included in two of the seven simulations we have analyzed. Although detections of high-redshift dwarf galaxies with the James Webb Space Telescope will be a challenge, studies of their fossil records in the local universe are promising because of their large spatial density.