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Cosmological Constraints from the Abundance of Weak-Lensing Shear-Selected Galaxy Clusters in the Hyper Suprime-Cam Subaru Strategic Program


Core Concepts
This research paper presents cosmological constraints derived from the abundance of galaxy clusters identified through weak gravitational lensing in data from the Hyper Suprime-Cam Subaru Strategic Program, offering a novel, gravity-based approach to understanding the universe's structure and evolution.
Abstract
  • Bibliographic Information: Chiu, I-Non et al. (2024). Weak-Lensing Shear-Selected Galaxy Clusters from the Hyper Suprime-Cam Subaru Strategic Program: II. Cosmological Constraints from the Cluster Abundance. Preprint. arXiv:2406.11970v2 [astro-ph.CO]

  • Research Objective: This study aims to constrain cosmological parameters, specifically Ωm and σ8, by analyzing the abundance of galaxy clusters selected using weak gravitational lensing data from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP).

  • Methodology: The researchers utilized weak-lensing data from the HSC-SSP to construct aperture-mass maps and identify galaxy clusters as peaks in these maps. They employed a truncated isothermal filter to minimize noise and a strict source selection process to avoid contamination from cluster member galaxies. The team then modeled the cluster abundance as a function of the weak-lensing signal-to-noise ratio, accounting for factors like the cluster mass profile, source redshift distribution, and weak-lensing mass bias. By comparing their model predictions to the observed cluster abundance, they derived constraints on cosmological parameters.

  • Key Findings: The analysis yielded constraints on key cosmological parameters, including Ωm = 0.50+0.28−0.24, σ8 = 0.685+0.161−0.088, and Ŝ8 ≡ σ8(Ωm/0.3)0.25 = 0.835+0.041−0.044 in a flat ΛCDM model. These findings demonstrate the feasibility of using weak-lensing shear-selected galaxy clusters for cosmological studies.

  • Main Conclusions: The study successfully demonstrates the use of weak-lensing shear-selected galaxy clusters as a robust and independent probe for cosmological parameters. The derived constraints are consistent with other cosmological probes, including those from the Cosmic Microwave Background and galaxy clustering, further strengthening their validity.

  • Significance: This research significantly advances the field of cosmology by establishing a novel and powerful method for constraining cosmological parameters using weak-lensing shear-selected galaxy clusters. This approach, being independent of baryonic tracers, offers a cleaner and potentially more accurate way to study the universe's large-scale structure and evolution.

  • Limitations and Future Research: The study acknowledges limitations such as the reliance on simulations for calibrating weak-lensing mass bias and the use of photometric redshifts for source galaxies. Future research with larger and deeper weak-lensing surveys like the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) will enable even more precise cosmological constraints and a deeper understanding of the universe's composition and evolution.

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Stats
The study used weak-lensing data from the HSC-Y3 dataset, covering an effective area of ≈500 deg2. The sample consists of 129 shear-selected clusters with a signal-to-noise ratio (ν) ≥ 4.7. The median redshift of the shear-selected clusters is ≈ 0.3. The lensing sources were selected at 𝑧≳0.7 with a median redshift of ≈ 1.3. The average shape noise (𝜎𝜅) is ≈ 0.70 across the six subfields.
Quotes
"Owing to the deep, wide-field, and uniform imaging of the HSC survey, this is by far the largest sample of shear-selected clusters, for which the selection solely depends on gravity and is free from any assumptions about the dynamical state and complex baryon physics." "This work realizes a cosmological probe utilizing weak-lensing shear-selected clusters and paves the way forward in the upcoming era of wide-field sky surveys."

Deeper Inquiries

How will upcoming wide-field sky surveys with even larger data sets and improved precision impact the use of weak-lensing shear-selected galaxy clusters for cosmological studies?

Upcoming wide-field sky surveys like the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST), Euclid, and the Roman Space Telescope promise to revolutionize the use of weak-lensing shear-selected galaxy clusters for cosmological studies. These surveys will acquire data with unprecedented depth, area coverage, and photometric redshift accuracy, leading to several significant advancements: Increased Sample Size and Redshift Range: The vast amount of data will enable the detection of orders of magnitude more shear-selected clusters, extending to higher redshifts. This will provide significantly tighter constraints on cosmological parameters, particularly those related to the evolution of dark energy and the growth of structure. Improved Mass Calibration: The higher number density of source galaxies and improved photometric redshifts will lead to more precise measurements of the weak-lensing signal, resulting in more accurate mass estimates for individual clusters. This will reduce the uncertainties in the mass-observable relation and improve the accuracy of cosmological constraints. Enhanced Understanding of Systematic Uncertainties: The larger sample size and wider redshift range will allow for more detailed studies of systematic uncertainties, such as those arising from baryonic effects, photometric redshift errors, and intrinsic cluster properties. This will enable the development of more robust and accurate methods for extracting cosmological information from shear-selected cluster samples. Combined Analyses with Other Probes: The rich datasets from these surveys will facilitate joint analyses of shear-selected clusters with other cosmological probes, such as galaxy clustering, cosmic shear, and the cosmic microwave background. These multi-probe analyses will break degeneracies between cosmological parameters and provide even stronger constraints on our cosmological model. In summary, upcoming wide-field sky surveys will usher in a new era for cluster cosmology using weak-lensing shear-selection. The increased statistical power, improved mass calibration, and enhanced understanding of systematic uncertainties will enable us to probe the Universe's structure formation history and the nature of dark energy with unprecedented precision.

Could systematic uncertainties arising from baryonic effects within galaxy clusters potentially impact the accuracy of the cosmological constraints derived from this method?

While weak-lensing shear-selected cluster cosmology boasts the advantage of being "baryonic-tracer-free" in its selection, systematic uncertainties arising from baryonic effects within galaxy clusters can still potentially impact the accuracy of the derived cosmological constraints. This is because baryonic processes, such as AGN feedback and star formation, can alter the distribution of matter within clusters, leading to deviations from the assumed dark matter-only profiles. Here's how baryonic effects can introduce systematic uncertainties: Impact on the Mass-Observable Relation: Baryonic processes can modify the relationship between the cluster mass and the observed weak-lensing signal. For instance, AGN feedback can expel gas from the cluster center, reducing the lensing signal and leading to an underestimate of the cluster mass. Alterations to the Halo Mass Function: Baryonic effects can also influence the halo mass function, which describes the abundance of clusters as a function of mass. This is because baryonic processes can affect the efficiency of halo formation and evolution. Deviations from NFW Profiles: The presence of baryons can cause deviations from the assumed NFW profiles used to model the cluster mass distribution. These deviations can introduce biases in the weak-lensing mass estimates. Mitigating these systematic uncertainties requires a multi-pronged approach: Improved Theoretical Modeling: Developing more sophisticated theoretical models that incorporate baryonic physics is crucial for accurately predicting the impact of these effects on the weak-lensing signal and the halo mass function. Hydrodynamical Simulations: High-resolution hydrodynamical simulations that include realistic baryonic physics are essential for calibrating the mass-observable relation and quantifying the impact of baryonic effects on cluster profiles. Multi-Wavelength Observations: Combining weak-lensing data with multi-wavelength observations, such as X-ray and Sunyaev-Zel'dovich effect measurements, can help constrain the gas distribution within clusters and improve the accuracy of mass estimates. By addressing these systematic uncertainties, we can ensure that weak-lensing shear-selected cluster cosmology remains a robust and powerful tool for constraining cosmological parameters.

How does the understanding of dark matter and dark energy, as informed by this research, influence our understanding of the ultimate fate of the universe?

Research on weak-lensing shear-selected galaxy clusters provides crucial insights into the properties of dark matter and dark energy, which in turn, shapes our understanding of the universe's ultimate fate. Here's how this research contributes: Constraining Dark Energy: The abundance and distribution of galaxy clusters are sensitive to the properties of dark energy, the mysterious force driving the accelerated expansion of the universe. By measuring the cluster abundance as a function of redshift, this research helps constrain the equation of state of dark energy, which describes its nature and evolution. This information is vital for understanding whether the universe's expansion will continue to accelerate, leading to a "Big Rip" scenario, or eventually slow down or reverse. Probing Dark Matter Properties: Weak-lensing shear-selection directly probes the total mass distribution in clusters, which is dominated by dark matter. By studying the cluster mass profiles and their evolution, researchers can constrain the properties of dark matter, such as its interaction cross-section and its clustering behavior. This information is crucial for understanding the role of dark matter in the formation of large-scale structures and its influence on the universe's evolution. Testing Cosmological Models: The cosmological constraints derived from this research, particularly on parameters like Ωm (matter density) and σ8 (matter clustering amplitude), are crucial for testing and refining our cosmological models. These models provide a framework for understanding the universe's evolution and predicting its ultimate fate. Current research suggests that the universe will likely continue to expand indefinitely, driven by dark energy. However, the exact fate remains uncertain, depending on the precise nature of dark energy and the future evolution of the universe. Continued research on weak-lensing shear-selected galaxy clusters, especially with upcoming surveys, will be crucial for obtaining more precise measurements of cosmological parameters and refining our understanding of the universe's destiny.
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