Redshift-space distortions from vector perturbations

TL;DR

This paper derives how vector perturbations influence redshift-space distortions in galaxy surveys, showing they affect correlation multipoles and can be constrained by future surveys like DESI and SKA.

Contribution

It provides a general expression for vector perturbations' effects on redshift-space distortions and assesses their detectability in upcoming galaxy surveys.

Findings

Vector perturbations contribute to the same multipoles as scalar ones.

Topological defects have a negligible impact on redshift-space distortions.

Future surveys can potentially measure vorticity induced by non-linear clustering.

Abstract

We compute a general expression for the contribution of vector perturbations to the redshift-space distortion of galaxy surveys. We show that they contribute to the same multipoles of the correlation function as scalar perturbations and should thus in principle be taken into account in data analysis. We derive constraints for next-generation surveys on the amplitude of two sources of vector perturbations, namely non-linear clustering and topological defects. While topological defects leave a very small imprint on redshift-space distortions, we show that the multipoles of the correlation function are sensitive to vorticity induced by non-linear clustering. Therefore future redshift surveys such as DESI or the SKA should be capable of measuring such vector modes, especially with the hexadecapole which appears to be the most sensitive to the presence of vorticity.