The cluster-galaxy cross-spectrum: an additional probe of cosmological and halo parameters

TL;DR

This paper demonstrates that incorporating cluster-galaxy cross-spectrum data in survey analyses significantly enhances constraints on cosmological parameters and halo models, especially improving sigma_8 estimates and halo occupation details.

Contribution

It introduces a Halo Model-based framework for the cluster-galaxy cross-spectrum and quantifies its benefit in constraining cosmological and halo parameters through Fisher analysis.

Findings

Adding cross-spectrum data doubles constraints on sigma_8.

Cross-spectrum helps tighten halo occupation distribution constraints.

Inclusion of cross-pairs improves dark energy figure-of-merit by 40%.

Abstract

There are several wide field galaxy and cluster surveys planned for the nearest future, e.g. BOSS, WFMOS, ADEPT, Hetdex, SPT, eROSITA. In the simplest approach one would analyze these independently, thus neglecting the extra information provided by the cluster-galaxy cross-pairs. In this paper we have focused on the possible synergy between these surveys by investigating the amount of information encoded in the cross-pairs. We present a model for the cluster-galaxy cross-spectrum within the Halo Model framework. To assess the gain in performance due to inclusion of the cluster-galaxy cross-pairs we carry out a Fisher matrix analysis for a BOSS-like galaxy redshift survey targeting luminous red galaxies and a hypothetical mass-limited cluster redshift survey with a lower mass threshold of 1.7x10^14 M_sun/h over the same volume. On small scales cluster-galaxy cross-spectrum probes directly density profile of the halos, instead of the density profile convolved with itself, as is the case for the galaxy power spectrum. Due to this different behavior, adding information from the cross-pairs helps to tighten constraints on the halo occupation distribution. By inclusion of the cross-pairs a factor of ~2 stronger constraints are obtained for sigma_8, while the improvement for the dark energy figure-of-merit is somewhat weaker: an increase by a factor of 1.4.