XV. A MODEL FOR THE EVOLUTION OF THE INTERGALACTIC MEDIUM

We studied the evolution of the intergalactic medium (IGM) in a cold dark-matter dominate universe. In the model the IGM is gravitationally coupled to the dark matter and is subject to protogalaxy heating and Compton and radiative coolings. Among the major results are: (1) The growth of the root-mean-square density fluctuations in the IGM is greatly reduced during the period of heating, but it picks up at late times as gravity dominates again. (2) The density contour plots show large connected structure in the IGM. (3) The power spectrum for the IGM on smaller scales grows slower than the power spectrum of the dark matter. The slope of the two-point correlation function for the IGM is similar to that of the observed galaxy-galaxy correlation function between separations 1 h-1^ < r < 3 h-1^ Mpc. (4) The amount of gas with temperatures below 104^ K is negligible, that between 104^ K and 105^ K is ~ 10%-20%, that between 105^ K and 106^ K ≥ 40%, and that above 106^ K ~ 40%. (5) The variation in pressure is ~10 times that in the temperature, suggesting no pressure equilibrium. Pressure is generally higher in regions of higher densities.