The SRG/eROSITA all-sky survey: Cosmology constraints from cluster abundances in the western Galactic hemisphere (2402.08458v2)

Abstract: The cluster mass function traces the growth of linear density perturbations and provides 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 {\it Spectrum Roentgen Gamma (SRG)} mission, launched in 2019, is to constrain cosmology through the evolution of cluster mass function. In this paper, we present the cosmological constraints obtained from 5259 clusters of galaxies detected over an area of 12791~deg$^2$ in the Western Galactic Hemisphere of the eROSITA's first All-Sky Survey (eRASS1). The common footprint region between the eROSITA Survey and DES, KiDS, and HSC surveys is used for calibration of the scaling between X-ray count rate and their total mass through measurements of their weak gravitational lensing signal. eRASS1 cluster abundances constrain the $\Lambda$CDM parameters, which are the energy density of the total matter to $\Omega_{\mathrm{m}}=0.29^{+0.01}_{-0.02}$, and the normalization of the density fluctuations to $\sigma_8=0.88\pm0.02$ and their combination yields $S_8=\sigma_8 (\Omega_\mathrm{m} / 0.3)^{0.5}=0.86\pm0.01$, consistent and at a similar precision with the state-of-the-art CMB measurements. eRASS1 cosmological experiment places a most stringent upper limit on the summed masses of left-handed light neutrinos to $\sum m_\nu< 0.22\mathrm{~eV}$ (95\% confidence interval). Combining eRASS1 cluster abundance measurements with CMB and ground-based neutrino oscillation experiments, we measure the summed neutrino masses to be $\sum m_\nu=0.08_{-0.02}^{+0.03}\mathrm{~eV}$ or $\sum m_\nu=0.12_{-0.01}^{+0.03}\mathrm{~eV}$ depending on the mass hierarchy scenario for neutrino eigenstates. eRASS1 cluster abundances significantly improve the constraints on the dark energy equation of state parameter to $w=-1.12\pm0.12$. (ABRIDGED)

• The paper derives cosmological parameters by analyzing the cluster mass function from 5259 eROSITA galaxy clusters calibrated with weak lensing data.
• It provides precise constraints on Ωm (0.29+0.01−0.02) and σ8 (0.88±0.02), and sets a stringent upper limit on the total neutrino mass (<0.43 eV).
• The study refines dark energy estimates by determining the equation of state parameter (w = –1.12±0.12), reinforcing the consistency of the ΛCDM model.

Analysis of Cosmological Constraints from the SRG/eROSITA All-Sky Survey Data

The research presented focuses on the cosmological implications derived from the SRG/eROSITA all-sky survey, specifically examining cluster abundances in the western Galactic hemisphere. The key goal of this paper is to extract cosmological parameters by analyzing the cluster mass function, which serves as a probe for understanding the evolution of density perturbations in the Universe.

Data and Methodology

The analysis utilizes data from 5259 galaxy clusters identified in the eROSITA survey's initial all-sky assessment. Through a synergy with optical data from the Dark Energy Survey (DES), Kilo-Degree Survey (KiDS), and Hyper Supreme Camera (HSC) survey, the researchers calibrate the relationship between X-ray count rates of clusters and their total masses. This calibration employs weak gravitational lensing signals to refine mass estimates, a crucial step for reducing biases traditionally associated with hydrostatic equilibrium assumptions in mass determination.

The cosmological parameters derived from this approach include the matter density parameter, $\Omega_{\mathrm{m}}$, and the normalization of density fluctuations, $\sigma_{8}$. This analysis yields $\Omega_{\mathrm{m}}=0.29^{+0.01}_{-0.02}$ and $\sigma_{8}=0.88\pm0.02$, results that align with measurements from state-of-the-art cosmic microwave background (CMB) experiments.

Significant Findings

The research also establishes a stringent upper limit on the summed mass of neutrinos, specifically $\sum m_{\nu}< 0.43\mathrm{~eV}$ at a 95% confidence level, based solely on cluster number counts. This is a notable advancement in constraining neutrino masses by leveraging galaxy cluster counts alone. Additionally, when combining eROSITA data with CMB observations and neutrino oscillation data, the paper estimates $\sum m_\nu = 0.09_{-0.02}^{+0.04}\mathrm{~eV}$ for a normal hierarchy in neutrino masses.

Furthermore, the eROSITA data facilitate advanced constraints on the dark energy equation of state parameter, yielding $w=-1.12 \pm 0.12$. Importantly, the results remain consistent within the framework of the ΛCDM cosmology, further validating the concordance model underpinning current cosmological theories.

Implications and Future Directions

The implications of these findings are substantial. The constraints on neutrino masses will inform next-generation neutrino experiments, providing tighter parameters for theoretical models of neutrino physics. Additionally, refined measurements of $\Omega_{\mathrm{m}}$ and $\sigma_{8}$ help reconcile previously observed tensions between large scale structures and CMB data, crucial for refining the parameters of the standard cosmological model.

Future work can expand on eROSITA's achievements by incorporating deeper all-sky surveys to enhance the precision of mass estimates. This will be crucial for probing dark energy dynamics and investigating potential deviations from Einstein's General Relativity on cosmic scales. The refinement of galaxy cluster-based methods will also enhance the accuracy of cosmological parameter extraction, supporting developments in both theoretical and observational astrophysics.