Quantification of the multi-streaming effect in Redshift Space Distortion

TL;DR

This paper measures and models the multi-streaming effect in redshift space distortion, demonstrating its impact on the Finger-of-God effect and improving RSD modeling for better cosmological constraints.

Contribution

It provides the first direct measurement of multi-streaming in RSD from simulations and offers a theoretical halo model explanation with a fitting formula.

Findings

Multi-streaming causes additional FoG damping in RSD.

Including multi-streaming improves RSD modeling accuracy.

The study helps break key degeneracies in RSD cosmology.

Abstract

Both multi-streaming (random motion) and bulk motion cause the Finger-of-God (FoG) effect in redshift space distortion (RSD). We apply a direct measurement of the multi-streaming effect in RSD from simulations, proving that it induces an additional, non-negligible FoG damping to the redshift space density power spectrum. We show that, including the multi-streaming effect, the RSD modelling is significantly improved. We also provide a theoretical explanation based on halo model for the measured effect, including a fitting formula with one to two free parameters. The improved understanding of FoG helps break the $f\sigma_8-\sigma_v$ degeneracy in RSD cosmology, and has the potential of significantly improving cosmological constraints.