Radiation Pressure in Lyman-alpha Forest Clouds
Abstract
The effective recombination coefficient, alphaeff, is refined for optically thin cases. Radiation pressure in Lyman-alpha and HeII Lyman-alpha is calculated in terms of the number density and the mean free path. Pressure equilibrium between Lyman-alpha clouds and an adiabatically expanding inter-galactic medium is assumed, ni Ti = nc Tc. Numerical models of isothermal and adiabatic expanding Lyman-alpha forest clouds are presented, including evolving UV sources (QSOs), with various turn-on times zon = 20, 10, and 5, and with q0 = 1/2 in a matter-dominated Friedmann-Robertson-Walker Universe. These models lead to the conclusion that the radiation pressure and QSO turn-on time are significant in determining the range of physical size, D, and neutral hydrogen column density, N(HI), permitted for stable Lyman-alpha forest clouds. This manuscript was written in 1989 and never submitted for publication.
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