Redshift-space correlation functions in large galaxy cluster surveys

TL;DR

This paper develops an analytical framework to model the redshift-space correlation functions of galaxy clusters, including distortions and covariance, to aid cosmological analysis in upcoming large surveys.

Contribution

It introduces explicit formulas for the monopole and higher multipoles of the redshift-space correlation function, accounting for distortions, shot-noise, and non-Gaussian effects.

Findings

Redshift-space distortions increase the monopole correlation by 10-20%.

The signal-to-noise ratio remains similar to real-space measurements.

Higher multipoles like the quadrupole are detectable in upcoming surveys like Euclid.

Abstract

Large ongoing and upcoming galaxy cluster surveys in the optical, X-ray and millimetric wavelengths will provide rich samples of galaxy clusters at unprecedented depths. One key observable for constraining cosmological models is the correlation function of these objects, measured through their spectroscopic redshift. We study the redshift-space correlation functions of clusters of galaxies, averaged over finite redshift intervals, and their covariance matrices. Expanding as usual the angular anisotropy of the redshift-space correlation on Legendre polynomials, we consider the redshift-space distortions of the monopole as well as the next two multipoles, $2\ell=2$ and 4. Taking into account the Kaiser effect, we developed an analytical formalism to obtain explicit expressions of all contributions to these mean correlations and covariance matrices. We include shot-noise and sample-variance effects as well as Gaussian and non-Gaussian contributions. We obtain a reasonable agreement with numerical simulations for the mean correlations and covariance matrices on large scales ($r> 10 h^{-1}$Mpc). Redshift-space distortions amplify the monopole correlation by about $10-20%$, depending on the halo mass, but the signal-to-noise ratio remains of the same order as for the real-space correlation. This distortion will be significant for surveys such as DES, Erosita, and Euclid, which should also measure the quadrupole $2\ell=2$. The third multipole, $2\ell=4$, may only be marginally detected by Euclid.