Using clusters in SZE + x-ray surveys as an ensemble of rulers to constrain cosmology

TL;DR

This paper proposes using galaxy clusters detected in SZE and x-ray surveys as a new method to measure cosmological distances, significantly improving dark energy constraints without extra observations.

Contribution

It introduces a novel approach of using cluster ensembles as rulers to estimate angular diameter distances, enhancing dark energy parameter constraints.

Findings

Using clusters as rulers improves dark energy constraints by factors of 1.5 to 4.

Adding mass calibration further tightens constraints by factors of 2 to 3.

Cluster-based distance measurements are comparable to supernovae in constraining cosmological parameters.

Abstract

Ongoing and upcoming surveys in x-rays and SZE are expected to jointly detect many clusters due to the large overlap in sky coverage. We show that, these clusters can be used as an ensemble of rulers to estimate the angular diameter distance, d_A(z). This comes at no extra observational cost, as these clusters form a subset of a much larger sample, assembled to build cluster number counts dn/dz. On using this d_A(z), the dark energy constraints can be improved by factors of 1.5 - 4, over those from just dn/dn. Even in the presence of a mass follow-up of 100 clusters (done for mass calibration), the dark energy constraints can be further tightened by factors of 2 - 3 . Adding d_A(z) from clusters is similar to adding d_L(z), from the SNe observations; for eg., dn/dn (from ACT/SPT) plus d_A(z) is comparable to dn/dz plus d_L(z) in constraining Omega_m and sigma_8.