Redshift-space correlation functions in large galaxy cluster surveys

¹ Institut de Physique Théorique, CEA Saclay, 91191 Gif-sur-Yvette, France
e-mail: patrick.valageas@cea.fr
² Max-Planck-Institut für extraterrestrische Physik (MPE), Giessenbachstrasse 1, 85748 Garching, Germany

Received: 22 May 2012
Accepted: 10 September 2012

Abstract

Context. 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.

Aims. 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, 2ℓ = 2 and 4.

Methods. 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.

Results. 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 2ℓ = 2. The third multipole, 2ℓ = 4, may only be marginally detected by Euclid.