Constraining Extended Reionization Models Through Arcminute-Scale CMB Measurements

The measurement of the optical depth to free electrons, tau_r, in the cosmic microwave background (CMB) provides an important constraint on reionization, but is degenerate to more complex reionization models. Small angular-scale CMB measurements of the kinetic Sunyaev-Zeldovich (kSZ) and Ostriker-Vishniac (OV) effects have the potential to break this degeneracy. We calculate the OV signal for various extended reionization histories described by a simple analytic form. These models are parametrized by dz, the duration of the reionization event. For reionization histories with identical values of tau_r, the OV amplitude at l = 3000 (C_3000) differs by ~20 % between the models with dz = 0.1 and dz = 3.0. We demonstrate that the removal of the z < 6 component of the OV signal will significantly enhance the ability to differentiate between reionization histories, with C_3000 varying by a factor of ~2 between the models with dz = 0.1 and dz = 3.0. If the low-redshift OV and related kSZ signal can be adequately subtracted, this would provide an important observational constraint on extended reionization models.