Reionization and small-scale fluctuations in the microwave background

It is shown that electron scattering off the moving ionized medium can regenerate arcminute fluctuations in almost all models of galaxy formation. Explicit calculations are presented for matter-dominated, Omega-0 = 1 cosmologies with hot dark matter and cold dark matter. Scaling arguments are also derived to show the size of this effect in models with Omega-0 less than 1, an epoch of radiation domination, or a sizable cosmological constant. In the first two cases, the fluctuations due to reionization scale as the amplitude of the perturbation spectrum to a power close to 2. In the last case, the fluctuations scale with the amplitude of the perturbation spectrum. This result depends on including terms that are second order in the amplitude of cosmological density perturbations, but the motions involved are strictly linear.