Constraining cosmology with pairwise velocity estimator

TL;DR

This paper develops a statistical method for the pairwise velocity estimator and applies it to Cosmicflows-2 data, constraining cosmological parameters and confirming consistency with standard cosmological models.

Contribution

It introduces a full statistical framework for the pairwise velocity estimator and demonstrates its application to real data for cosmological constraints.

Findings

Constraints are consistent with WMAP and Planck cosmologies.

No evidence found for modified gravity or dynamic dark energy.

Current data precision is insufficient to challenge ΛCDM.

Abstract

In this paper, we develop a full statistical method for the pairwise velocity estimator previously proposed, and apply Cosmicflows-2 catalogue to this method to constrain cosmology. We first calculate the covariance matrix for line-of-sight velocities for a given catalogue, and then simulate the mock full-sky surveys from it, and then calculate the variance for the pairwise velocity field. By applying the $8315$ independent galaxy samples and compressed $5224$ group samples from Cosmicflows-2 catalogue to this statistical method, we find that the joint constraint on $\Omega^{0.6}_{\rm m}h$ and $\sigma_{8}$ is completely consistent with the WMAP 9-year and Planck 2015 best-fitting cosmology. Currently, there is no evidence for the modified gravity models or any dynamic dark energy models from this practice, and the error-bars need to be reduced in order to provide any concrete evidence against/to support $\Lambda$CDM cosmology.