@article{17828, abstract = {We quantify the consequences of intergalactic dust produced by the first Type II supernovae in the universe. The fraction of gas converted into stars is calibrated based on the observed C/H ratio in the intergalactic medium at z = 3, assuming a Scalo mass function for the stars. The associated dust absorbs starlight energy and emits it at longer wavelengths. For a uniform mix of metals and dust with the intergalactic gas, we find that the dust distorts the microwave background spectrum by a y-parameter in the range (0.06-6) × 10-5 (MSN/0.3 M☉), where MSN is the average mass of dust produced per supernova. The opacity of intergalactic dust to infrared sources at redshifts of z ≳ 10 is significant, τdust = (0.1-1) × (MSN/0.3 M☉), and could be detected with the Next Generation Space Telescope. Although dust suppresses the Lyα emission from early sources, the redshifts of star clusters at z = 10-35 can be easily inferred from the Lyman limit break in their infrared spectrum between 1 and 3.5 μm.}, author = {Loeb, Abraham and Haiman, Zoltán}, issn = {1538-4357}, journal = {The Astrophysical Journal}, number = {2}, pages = {571--576}, publisher = {American Astronomical Society}, title = {{Signatures of intergalactic dust from the first supernovae}}, doi = {10.1086/304919}, volume = {490}, year = {1997}, } @article{17848, abstract = {The high ionization level and nonzero metallicity (~1% Z☉) of the intergalactic gas at redshifts z ≲ 5 implies that nonlinear structure had started to form in the universe at earlier times than we currently probe. In cold dark matter (CDM) cosmologies, the first generation of baryonic objects emerges at redshifts z ~ 10-50. Here we examine the observable consequences of the possibility that an early generation of stars reionized the universe and resulted in the observed metallicity of the Lyα forest. Forthcoming microwave anisotropy experiments will be sensitive to the damping of anisotropies caused by scattering off free electrons from the reionization epoch. For a large range of CDM models with a Scalo stellar mass function, we find that reionization occurs at a redshift z ≳ 10 and damps the amplitude of anisotropies on angular scales ≲10° by a detectable amount, ~10%-25%. However, reionization is substantially delayed if the initial stellar mass function transformed most of the baryons into low-mass stars. In this case, the mass fraction of pregalactic stars could be constrained from the statistics of microlensing events in galactic halos or along lines of sight to quasars. Deep infrared imaging with future space telescopes (such as the Space Infrared Telescope Facility or the Next Generation Space Telescope) will be able to detect bright star clusters at z ≳ 5. The cumulative bremsstrahlung emission from these star clusters yields a measurable distortion to the spectrum of the microwave background.}, author = {Haiman, Zoltán and Loeb, Abraham}, issn = {1538-4357}, journal = {The Astrophysical Journal}, number = {1}, pages = {21--37}, publisher = {American Astronomical Society}, title = {{Signatures of stellar reionization of the universe}}, doi = {10.1086/304238}, volume = {483}, year = {1997}, } @article{17822, abstract = {We investigate the formation of molecular hydrogen (H_2_) in a primordial H + He gas cloud irradiated by a power-law UV flux. We find that at high densities (~>1 cm^-3^) and low temperatures (<~10^4^ K), the background radiation enhances the formation of H_2_ and results in molecular cooling dominating over photoionization heating. This process could accelerate the collapse and fragmentation of dense objects at high redshifts.}, author = {Haiman, Zoltán and Rees, Martin J. and Loeb, Abraham}, issn = {1538-4357}, journal = {The Astrophysical Journal}, publisher = {American Astronomical Society}, title = {{H 2 cooling of primordial gas triggered by UV irradiation}}, doi = {10.1086/177628}, volume = {467}, year = {1996}, } @article{17834, abstract = {We investigate the early formation of bound objects with masses comparable to the cosmological Jeans mass (~10^5^ M_sun_). We follow the growth of isolated spherically symmetric density peaks starting from the linear perturbative regime. The initial parameters correspond to density peaks of various widths and heights in a cold dark matter cosmology. We use a one-dimensional spherical Lagrangian hydrodynamics code to follow the dynamical, thermal, and nonequilibrium chemical evolution of the gas. The system includes a collisionless dark matter component and a baryonic component composed of the nine species H, H^-^, H^+^, He, He^+^, He^++^, H_2_, H_2_^+^, and e^-^. All relevant chemical reactions between these species and their cooling mechanisms are included in the calculations. We explore the dependence of the dynamical evolution of the gas on two parameters: the initial mass scale and the initial overdensity of the system. We follow the evolution of the density, temperature, and abundance profiles within the cloud, assuming two types of central boundary conditions for the collisionless component: in one the infalling dark matter virializes through a reflection from a hard sphere, while in the other it accretes onto a central sink. We find that in both cases, radiative cooling by H_2_ affects the collapse dynamics of the gas only after it has already virialized and become part of the bound object. Therefore, radiative cooling is unlikely to have triggered the initial collapse of perturbations at redshifts z > 10. Nevertheless, baryonic objects with masses well below the linear theory Jeans mass (<~10^3^ M_sun_) form at high redshifts because of shell crossing by the dark matter. Such objects could be the progenitors of a primordial population of high-mass stars in the intergalactic medium.}, author = {Haiman, Zoltán and Thoul, Anne A. and Loeb, Abraham}, issn = {1538-4357}, journal = {The Astrophysical Journal}, publisher = {American Astronomical Society}, title = {{Cosmological formation of low-mass objects}}, doi = {10.1086/177343}, volume = {464}, year = {1996}, }