A Semi-Analytic Model for Cosmological Reheating and Reionization Due to the Gravitational Collapse of Structure

Abstract

We present a semi-analytic model for the thermal and ionization history of the universe at 1000 >~ z >~ 3. This model incorporates much of the essential physics included in full-scale hydrodynamical simulations, such as (1) gravitational collapse and virialization; (2) star/quasar formation and subsequent ionizing radiation; (3) heating and cooling; (4) atomic and molecular physics of hydrogen; and (5) the feedback relationships between these processes. In addition, we model the process of reheating and reionization using two separate phases, self-consistently calculating the filling factor of each phase. Thus radiative transfer is treated more accurately than simulations to date have done: we allow to lowest order for both the inhomogeneity of the sources and the sinks of radiation. After calibrating and checking the results of this model against a hydrodynamical simulation, we apply our model to a variety of Gaussian and non-Gaussian CDM-dominated cosmological models. Our major conclusions include: (1) the epoch of reheating depends most strongly on the power spectrum of density fluctuations at small scales; (2) because of the effects of gas clumping, full reionization occurs at z ~ 10 in all models; (3) the CMBR polarization and the stars and quasars to baryons ratio are strong potential discrimants between different assumed power spectra; (4) the formation of galactic spheroids may be regulated by the evolution of reheating through feedback, so that the Jeams mass tracks the non-linear mass scale; and (5) the evolution of the bias of luminous objects can potentially discriminate strongly between Gaussian and non-Gaussian PDFs.