Statistics – Computation
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt.........8g&link_type=abstract
Ph.D. Thesis Texas Univ., Austin.
Statistics
Computation
3
Cosmology, Dark Matter, Galactic Evolution, Intergalactic Media, Interstellar Gas, Photoionization, Absorption Spectra, Astronomical Models, Baryons, Computational Astrophysics, Density Distribution, Energy Dissipation, Quasars, Radiative Transfer, Red Shift, Thermal Energy
Scientific paper
We have calculated in detail the thermal and ionization evolution of a uniform intergalactic medium (IGM) composed of H and He, undergoing 'reionization' in a post-recombination Friedmann universe, including the mean effect of gas clumps embedded in a smoothly distributed ambient gas. We have solved nonequilibrium rate equations for ionization and recombination, together with the equations of energy conservation, including the effects of cosmological expansion, radiative and Compton cooling, and the diffuse flux emitted by the gas, and radiative transfer. We have included the contribution to the continuum opacity of the universe due to the observed quasar absorption line clouds (QALC's). We have considered a variety of generic sources of photoionization, including quasars and primeval galaxies, as well as the possibility that hydrodynamical processes deposit thermal energy in the IGM. Our purpose is to elucidate the minimum requirements for reionizing the IGM by z approx. = 5 to the extent required by the Gunn-Peterson limit, by the energy release associated with cosmological structure formation. These minimum requirements are a significant constraint on theories of the origin of structure in the universe. We have calculated the time varying density of the IGM by coupling our detailed, numerical calculations of an evolving uniform IGM to the linearized equations for the growth of density fluctuations in both the gaseous and dark components in a Cold Dark Matter (CDM) universe, identifying the IGM density with the uncollapsed baryon fraction. The collapsed fraction is postulated to be a source of energy injection into the IGM by radiation or bulk hydrodynamical heating (e.g. via shocks) or both, at a rate which is marginally enough to satisfy the Gunn-Peterson constraint at z less than 5. We find that the IGM must have contained a substantial fraction of the total baryon density of the universe in a CDM model both during and after its reionization epoch. Self-consistent reionization of the IGM by the collapsed baryon fraction has a strong effect on the rate of collapse.
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