The SRG/eROSITA All-Sky Survey
R. Seppi, Johan Comparat, V. Ghirardini, C. Garrel, E. Artis, Ariel G. Sánchez, Ang Liu, N. Clerc, Esra Bülbül, S. Grandis, Matthias Kluge, T. H. Reiprich, A. Merloni, Xiaoyuan Zhang, Y. E. Bahar, Soumya Shreeram, J. S. Sanders, M. E. Ramos-Ceja, M. Krumpe
Abstract
Context. The spatial distribution of galaxy clusters provides a reliable tracer of the large-scale distribution of matter in the Universe. The clustering signal depends on intrinsic cluster properties and cosmological parameters. Aims. The ability of eROSITA on board Spectrum-Roentgen-Gamma (SRG) to discover galaxy clusters allows the association of extended X-ray emission with dark matter haloes to be probed. We measured the projected two-point correlation function to study the occupation of dark matter haloes by clusters and groups detected by the first eROSITA all-sky survey (eRASS1). Methods. We created five volume-limited samples probing clusters with different redshifts and X-ray luminosity values. We interpreted the correlation function with halo occupation distribution (HOD) and halo abundance matching (HAM) models. We simultaneously fit the cosmological parameters and halo bias of a flux-limited sample of 6493 clusters with purity > 96%. Results. We obtained a detailed view of the halo occupation for eRASS1 clusters. The fainter population at low redshift (S0: L̄ X = 4.63 × 10 43 erg s −1 , 0.1 < z < 0.2) is the least biased compared to dark matter, with b = 2.95 ± 0.21. The brightest clusters up to higher redshift (S4: L̄ X = 1.77 × 10 44 erg s −1 , 0.1 < z < 0.6) exhibit a higher bias b = 4.34 ± 0.62. Satellite groups are rare, with a satellite fraction < 14.9% (8.1) for the S0 (S4) sample. We combined the HOD prediction with a HAM procedure to constrain the scaling relation between L X and mass in a new way, and find a scatter of ⟨ σ Lx ⟩ = 0.36. We obtain cosmological constraints for the physical cold dark matter density ω c = 0.12 −0.02 +0.03 and an average halo bias b = 3.63 −0.85 +1.02 . Conclusions. We modelled the clustering of galaxy clusters with a HOD approach for the first time, paving the way for future studies combining eROSITA with 4MOST, SDSS, Euclid , Rubin , and DESI to unravel the cluster distribution in the Universe.