arXiv subjects

Zoltan Haiman

Publications and source records attributed to Zoltan Haiman.

241 records · Page 14Linked to original sources

arXiv1997

Signatures of Stellar Reionization of the Universe

The high ionization level and universal metallicity (1% solar) 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 Lyman-alpha 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 degrees by a detectable amount, of order 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 pre-galactic 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 SIRTF 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.

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arXiv1997

Detection of the First Star Clusters With NGST

We calculate the observable signatures of the first generation of stars at high redshift (5 10) within its 4'x4' field of view. If stars occupy a region comparable to the virial radius of the cluster, then 1% of these clusters could be resolved. We calculate the expected number-flux relation and angular size distribution for these early star clusters. We also describe the reionization of the IGM due to the first generation of stars, and the consequent damping of the CMB anisotropies on small angular scales. This damping could be detected below 10 degree angular scales by MAP and PLANCK.

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arXiv1997

Signatures of Intergalactic Dust From the First Supernovae

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 (0.02-2)x10^{-5}(M_d/0.3M_sun), where M_d is the average mass of dust produced per supernova. The opacity of intergalactic dust to infrared sources at redshifts z>10 is significant, tau=(0.1-1)x(M_d/0.3M_sun), and could be detected with the Next Generation Space Telescope. Although dust suppresses the Ly-alpha 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 1-3.5 micron.

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arXiv1997

Formation and Signatures of the First Stars

We use a spherical hydrodynamics code to show that in cold dark matter cosmologies, the first stars form at z=50 through the direct collapse of gas in low-mass systems (approx 10^4 solar masses). Photons from the first stars easily photodissociate the molecular hydrogen throughout the universe and so molecular cooling does not affect the subsequent fragmentation of gas clouds into stars. We examine observable signatures of the pre-galactic population of stars. These include the detected metallicity and photo-ionization of the intergalactic medium, and the soon to be detected damping of microwave anisotropies on small angular scales (< 10 degrees). The Next Generation Space Telescope will be able to directly image the pre-galactic star clusters, while the DIMES experiment could detect their Bremsstrahlung emission.

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arXiv1996

Destruction of Molecular Hydrogen During Cosmological Reionization

We investigate the ability of primordial gas clouds to retain molecular hydrogen (H_2) during the initial phase of the reionization epoch. We find that before the Stromgren spheres of the individual ionizing sources overlap, the UV background below the ionization threshold is able to penetrate large clouds and suppress their H_2 abundance. The consequent lack of H_2 cooling could prevent the collapse and fragmentation of clouds with virial temperatures T_vir < 10^4 K (or masses 10^8 Msun [(1+z_vir)/10]^{-3/2}). This negative feedback on structure-formation arises from the very first ionizing sources, and precedes the feedback due to the photoionization heating.

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arXiv1995

H_2 Cooling of Primordial Gas Triggered by UV Irradiation

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.

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arXiv1995

Cosmological Formation of Low-Mass Objects

We investigate the early formation of bound objects with masses comparable to the cosmological Jeans mass (10^5 solar masses). 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 non-equilibrium 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 find that 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, objects with baryonic masses well below the linear-theory Jeans mass (<10^3 solar masses) collapse due to shell crossing by the dark matter. Such objects could be the progenitors of a primordial population of high-mass stars in the intergalactic medium.

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