Power spectrum of the CODEX clusters

¹ Department of Physics, University of Helsinki, PO Box 64 00014 Helsinki, Finland
² Helsinki Institute of Physics, University of Helsinki, Gustaf Hällströmin katu 2, Helsinki, Finland
³ Instituto de Astrofísica de Canarias, s/n, E-38205 La Laguna, Tenerife, Spain
⁴ Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
⁵ INAF-Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, 34143 Trieste, Italy
⁶ INFN, Sezione di Trieste, Via Valerio 2, 34127 Trieste, TS, Italy
⁷ IFPU, Institute for Fundamental Physics of the Universe, Via Beirut 2, 34151 Trieste, Italy

^⋆ Corresponding author: valtteri.lindholm@helsinki.fi

Received: 11 December 2024
Accepted: 19 March 2025

Abstract

Aims. We analyze the clustering of galaxy clusters in a large contiguous sample, the Constrain Dark Energy with X-ray (CODEX) sample. We construct a likelihood for cosmological parameters by comparing the measured clustering signal and a theoretical prediction, and use this to obtain parameter constraints.

Methods. We measured the three multipole moments (monopole, quadrupole, and hexadecapole, ℓ = 0, 2, 4) of the power spectrum of a subset of the CODEX clusters. To fully model cluster clustering, we also determined the expected clustering bias of the sample using estimates for the cluster masses and a mass-to-bias model calibrated using N-body simulations. We estimated the covariance matrix of the measured power spectrum multipoles using a set of simulated dark-matter halo catalogs. Combining all these ingredients, we performed a Markov chain Monte Carlo sampling of cosmological parameters Ω_m and σ₈ to obtain their posterior.

Results. We found the CODEX clustering signal to be consistent with an earlier X-ray selected cluster sample, the REFLEX II sample. We also found that the measured power spectrum multipoles are compatible with the predicted, bias-scaled linear matter power spectrum when the cosmological parameters determined by the Planck satellite are assumed. Furthermore, we found the marginalized parameter constraints of Ω_m = 0.24_−0.04^+0.06 and σ₈ = 1.13_−0.24^+0.43. The full 2D posterior is consistent, for example, with the Planck cosmology within the 68% confidence region.