The SRG/eROSITA all-sky survey

Cosmology constraints from cluster abundances in the western Galactic hemisphere

¹ Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse 1, 85748 Garching, Germany
² IRAP, Université de Toulouse, CNRS, UPS, CNES, 31028 Toulouse, France
³ Universität Innsbruck, Institut für Astro- und Teilchenphysik, Technikerstr. 25/8, 6020 Innsbruck, Austria
⁴ Department of Physics, National Cheng Kung University, 70101 Tainan, Taiwan
⁵ Universitäts-Sternwarte, Faculty of Physics, LMU Munich, Scheinerstr. 1, 81679 München, Germany
⁶ Arnold Sommerfeld Center for Theoretical Physics, LMU Munich, Theresienstr. 37, 80333 München, Germany
⁷ Department of Physical Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan
⁸ Argelander-Institut für Astronomie (AIfA), Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
⁹ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
¹⁰ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
¹¹ McWilliams Center for Cosmology, Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213, USA
¹² Subaru Telescope, National Astronomical Observatory of Japan, 650 N Aohoku Place Hilo HI 96720 USA
¹³ Kobayashi-Maskawa Institute for the Origin of Particles and the Universe (KMI), Nagoya University, Nagoya 464-8602, Japan
¹⁴ Institute for Advanced Research, Nagoya University, Nagoya 464-8601, Japan
¹⁵ Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study (UTIAS), The University of Tokyo, Chiba 277-8583, Japan

Received: 5 December 2023
Accepted: 17 June 2024

Abstract

The evolution of the cluster mass function traces the growth of linear density perturbations, providing valuable insights into the growth of structures, the nature of dark matter, and the cosmological parameters governing the Universe. The primary science goal of eROSITA, on board the Spectrum Roentgen Gamma (SRG) mission, is to constrain cosmology through the evolution of the cluster mass function. In this paper, we present a set of cosmological constraints obtained from 5259 clusters of galaxies detected over an area of 12791 deg² in the western Galactic hemisphere of eROSITA’s first All-Sky Survey (eRASS1). The common footprint region (4968 deg²) between the eROSITA Survey and Dark Energy Survey (DES), the Kilo-Degree Survey (KiDS), and the Hyper Supreme Camera (HSC) survey is used for calibration of the scaling between X-ray count rate of the clusters and their total mass through measurements of their weak gravitational lensing signal. The eRASS1 cluster abundances constrain the ΛCDM parameters, namely, the energy density of the total matter to Ω_m = 0.29_−0.02^+0.01 and the normalization of the density fluctuations to σ₈ = 0.88 ± 0.02, and their combination yields S₈ = σ₈(Ω_m/0.3)^0.5 = 0.86 ± 0.01. These results are consistent and achieve at a similar precision with state-of-the-art cosmic microwave background (CMB) measurements. Furthermore, the eRASS1 cosmological experiment places a most stringent upper limit on the summed masses of left-handed light neutrinos to ∑ m_v < 0.43 eV (95% confidence interval) from cluster number counts alone. By combining eRASS1 cluster abundance measurements with CMB- and ground-based neutrino oscillation experiments, we measured the summed neutrino masses to be ∑ m_v = 0.09_−0.02^+0.04 eV or ∑ m_v = 0.12_−0.02^+0.03 eV, assuming a normal or inverted mass hierarchy scenario for neutrino eigenstates. The eRASS1 cluster abundances significantly improve the constraints on the dark energy equation of state parameter to w = −1.12 ± 0.12. When ∑ m_v and w are left free, we find consistent results with the concordance ΛCDM cosmology. Our results from the first All-Sky Survey improve the cosmological constraints by over a factor of 5 to 9 over the previous cluster surveys, establishing cluster abundance measurements for precision cosmology and setting the stage for deeper eROSITA All-Sky Surveys, as well as for future cluster abundance experiments.