CALCULATION OF THE OSTRIKER-VISHNIAC EFFECT IN COLD DARK-MATTER MODELS - ART. NO. 043001

We present a new derivation of the cosmic microwave background anisotr opy spectrum from the Ostriker-Vishniac effect for an open, flat, or c losed universe, and calculate the anisotropy expected in cold dark mat ter (CDM) models. We provide simple semi-analytic fitting formulas for the Vishniac power spectrum that can be used to evaluate the expected anisotropy in CDM models for any arbitrary ionization history. In a f lat universe, CDM models normalized to cluster abundances produce rms temperature anisotropies of 0.8-2.4 mu K on arcminute angular scales f or a constant ionization fraction of unity, whereas an ionization frac tion of 0.2 yields rms anisotropies of 0.3-0.8 mu K. In an open and/or high-baryon-density universe, the level of anisotropy is somewhat hig her. The signal in some of these models may be detectable with planned interferometry experiments. The damping of the acoustic peaks in the primary-anisotropy spectrum at degree angular scales depends primarily on the optical depth and only secondarily on the epoch of reionizatio n. On the other hand, the amplitude of Ostriker-Vishniac anisotropies depends sensitively on the epoch of reionization. Therefore, when comb ined with the estimate of the reionization optical depth provided by m aps of degree-scale anisotropies, the Ostriker-Vishniac effect can pro vide a unique probe of the epoch of reionization.