Beyond the Damping Tail: Cross‐Correlating the Kinetic Sunyaev‐Zel’dovich Effect with Cosmic Shear

Abstract

Secondary anisotropies of the cosmic microwave background (CMB) have the potential to reveal intricate details about the history of our universe between the present and recombination epochs. However, because the CMB we observe is the projected sum of a multitude of effects, the interpretation of small-scale anisotropies by future high-resolution experiments will be marred by uncertainty and speculation without the handles provided by other observations. The recent controversy over the excess small-scale anisotropy detected by CBI and the BIMA array is a foretaste of potential challenges that will be faced when interpreting future experiments. In this paper we show that cross-correlating the CMB with an overlapping weak-lensing survey will isolate the elusive kinetic Sunyaev-Zel'dovich (kSZ) effect from secondary anisotropies generated at higher redshifts. We show that if upcoming high angular resolution CMB experiments, like Planck/ACT/SPT, cover the same area of sky as current and future weak-lensing surveys, like CFTHLS/SNAP/LSST, the cross-correlation of cosmic shear with the kSZ effect will be detected with high signal-to-noise ratio, increasing the potential science accessible to both sets of surveys. For example, if ACT and a CFHTLS-like survey were to overlap, this cross-correlation would be detected with a total signal-to-noise ratio greater than 220, reaching 1.8 per individual multipole around l ~ 5000. Furthermore, this cross-correlation probes the three-point coupling between the underlying dark matter and the momentum of the ionized baryons in the densest regions of the universe at intermediate redshifts. Similar to the thermal Sunyaev-Zel'dovich (tSZ) power spectrum, its strength is extremely sensitive to the power spectrum normalization parameter, σ8, scaling roughly as σ. It provides an effective mechanism to isolate any component of anisotropy due to patchy reionization and rule out primordial small-scale anisotropy.