Reconstructing cosmic growth with kSZ observations in the era of Stage IV experiments

TL;DR

This paper proposes a method to measure the cosmic growth rate with sub-1% precision up to redshift 1 using kSZ observations from future CMB experiments, improving constraints on structure formation.

Contribution

It introduces a novel blind constrained realization method for separating kSZ signals, enhancing measurement accuracy over traditional aperture photometry techniques.

Findings

Potential to measure the growth and expansion rate product to better than 1% accuracy up to z≈1.

Demonstrates that Stage 4 CMB experiments can achieve competitive constraints with galaxy surveys.

Shows that combining kSZ and tSZ measurements effectively breaks degeneracies in velocity and optical depth.

Abstract

Future ground-based CMB experiments will generate competitive large-scale structure datasets by precisely characterizing CMB secondary anisotropies over a large fraction of the sky. We describe a method for constraining the growth rate of structure to sub-1% precision out to $z\approx 1$, using a combination of galaxy cluster peculiar velocities measured using the kinetic Sunyaev-Zel'dovich (kSZ) effect, and the velocity field reconstructed from galaxy redshift surveys. We consider only thermal SZ-selected cluster samples, which will consist of $\mathcal{O}(10^4-10^5)$ sources for Stage 3 and 4 CMB experiments respectively. Three different methods for separating the kSZ effect from the primary CMB are compared, including a novel blind "constrained realization" method that improves signal-to-noise by a factor of $\sim 2$ over a commonly-used aperture photometry technique. Measurements of the integrated tSZ $y$-parameter are used to break the kSZ velocity-optical depth degeneracy, and the effects of including CMB polarization and SZ profile uncertainties are also considered. A combination of future Stage 4 experiments should be able to measure the product of the growth and expansion rates, $\alpha\equiv f H$, to better than 1% in bins of $\Delta z = 0.1$ out to $z \approx 1$ -- competitive with contemporary redshift-space distortion constraints from galaxy surveys.