A semianalytic model for cosmological reheating and reionization due to the gravitational collapse of structure

We present a semianalytic model for the thermal and ionization history of the universe at 1000 greater than or similar to z greater than or similar to 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 published to date have done: we allow to lowest order for 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 (adiabatic power spectral and non-Gaussian (texture and isocurvature) cold dark matter (CDM)-dominated cosmologies normalized to cluster abundances. Our model is also normalized to observations of the ionizing UV intensity J(21) approximate to 1 at redshift z = 4. Our major conclusions include: (1) the epoch of reheating (starting late at z similar to 30 or early at z similar to 80) depends most strongly on the power spectrum (late: adiabatic; early: texture or isocurvature); (2) because of the effects of gas clumping, full reionization occurs at z similar to 10 in all models; (3) the cosmic microwave background radiation (CMBR) polarization anisotropy will be a strong discriminant between late and early reheating models; (4) the fraction of baryons sequestered in stars and quasars in early reheating models appears to be greater than the observational limit, while the fraction in late reheating models is well. below it; (5) the average degree of nonlinearity for collapsing baryons remains roughly constant during reheating, a possible explanation of which is feedback, which regulates the pace of reheating through the Jeans criterion; and (6) the evolution of the bias of luminous objects can potentially discriminate strongly between Gaussian and non-Gaussian probability density functions.