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We investigate the physical conditions for the growth of intermediate-mass seed black holes assumed to have formed from remnants of the first generation of massive stars. We follow the collapse of high s halos with Tvir > 104 K using cosmological, smooth-particle hydrodynamic (SPH) simulations in the standard LCDM model. During the collapse of the parent halo, the seed holes are incorporated through mergers into larger systems and accrete mass from the surrounding gas. We include a self-consistent treatment of star formation, black hole accretion, and associated feedback processes. Even under optimistic assumptions for the seed black hole mass and for efficient merger rates, we find that seed holes in halos M [?] 1010 M never reach the conditions for critical Eddington growth. Most of the black hole growth in this regime is determined by the initial mass and the merger rates. Critical accretion rates are reached, albeit only after a significant delay, at the time of collapse (z ~ 7) for 3-4 s halos of M ~ 1011 M. Our results imply MBH = 5 x 106 M (Mhalo/1011 M)0.78 at the time of collapse. The required conditions of Eddington growth to explain the buildup of supermassive black holes (~109 M), as implied by Sloan quasars at z > 6, are therefore hard to meet in such a scenario. Without a "jump start," these conditions may be only achieved in extremely rare halos with Mhalo > 1013 that collapsed before z ~ 6. The sub-Eddington regime in which black holes accrete at early time implies a small contribution to the reionization by miniquasar but still sufficient to cause appreciable heating of the IGM at z [?] 15-18.

We use numerical simulations of hydrogen reionization by stellar sources in the context of LCDM cosmogonies to investigate the 21 (1 + z) cm radio signal expected from the diffuse intergalactic medium (IGM) prior to the epoch of reionization breakthrough at redshift zion. Two reionization scenarios are analyzed in detail: an "early reionization" case with zion [?] 13, consistent with the recent discovery by the Wilkinson Microwave Anisotropy Probe (WMAP) satellite of a large optical depth to Thomson scattering, and a "late reionization" case with zion [?] 8. It is a generic prediction of these models that the background of Lya photons produced by the early generation of stars which ultimately ionize the universe will be sufficiently intense to make intergalactic neutral hydrogen visible against the cosmic microwave background during the "gray age," i.e., zion [?] z [?] 20. Depending on the redshift of reionization breakthrough, broad-beam observations at frequencies [?]150 MHz (below 100 MHz for the early reionization scenario) with the next generation of radio telescopes should reveal angular fluctuations in the sky brightness temperature in the range 5-20 mK (1 s) on scales below 5'.

In this talk I will present a model for primordial galaxy formation. In particular, I will review the feedback effects that regulate the process: (i) radiative (i.e. ionizing and H2-photodissociating photons) and (ii) stellar (i.e. SN explosions) feedback produced by massive stars. I will also address how the IGM reionization can be influenced by this population of primordial galaxies and describe a Monte Carlo method for the radiative transfer of ionizing photons through the IGM.

If gamma-ray bursts (GRBs) occur at high redshifts, then their bright afterglow emission can be used to probe the ionization and metal enrichment histories of the intervening intergalactic medium during the epoch of reionization. In contrast to other sources, such as galaxies or quasars, which fade rapidly with increasing redshift, the observed infrared flux from a GRB afterglow at a fixed observed age is only a weak function of its redshift. This results from a combination of the spectral slope of GRB afterglows and the time stretching of their evolution in the observer's frame. Assuming that the GRB rate is proportional to the star formation rate and that the characteristic energy output of GRBs is ~1052 ergs, we predict that there are always ~15 GRBs from redshifts z [?] 5 across the sky that are brighter than ~100 nJy at an observed wavelength of ~2 mm. The infrared spectrum of these sources could be taken with the future Next Generation Space Telescope as a follow-up to early X-ray localization with the Swift satellite.

We study the effects of the ionizing and dissociating photons produced by Population III objects on the surrounding intergalactic medium. We find that the typical size of an H2 photodissociated region, Rd [?] 1-5 kpc, is smaller than the mean distance between sources at z [?] 20-30 but larger than the ionized region by a factor depending on the detailed properties of the emission spectrum. This implies that clearing of intergalactic H2 occurs before reionization of the universe is complete. In the same redshift range, the soft-UV background in the Lyman-Werner bands, when the intergalactic H and H2 opacity is included, is found to be JLW [?] 10-30 to 10-27 ergs cm-2 s-1 Hz-1. This value is well below the threshold required for the negative feedback of Population III objects on the subsequent galaxy formation to be effective in that redshift range.

We study the effects of the ionizing and dissociating photons produced by Population III objects on the surrounding intergalactic medium. We find that the typical size of an H2photodissociated region, Rd? 1-5 kpc, is smaller than the mean distance between sources at z? 20-30 but larger than the ionized region by a factor depending on the detailed properties of the emission spectrum. This implies that clearing of intergalactic H2occurs before reionization of the universe is complete. In the same redshift range, the soft-UV background in the Lyman-Werner bands, when the intergalactic H and H2opacity is included, is found to be JLW? 10-30to 10-27ergs cm-2s-1Hz-1. This value is well below the threshold required for the negative feedback of Population III objects on the subsequent galaxy formation to be effective in that redshift range.