KiDS-1000 Cosmology: Cosmic shear constraints and comparison between two point statistics (2007.15633v2)

Abstract: We present cosmological constraints from a cosmic shear analysis of the fourth data release of the Kilo-Degree Survey (KiDS-1000), doubling the survey area with nine-band optical and near-infrared photometry with respect to previous KiDS analyses. Adopting a spatially flat $\Lambda$CDM model, we find $S_8 = \sigma_8 (\Omega_{\rm m}/0.3)^{0.5} = 0.759^{+0.024}_{-0.021}$ for our fiducial analysis, which is in $3\sigma$ tension with the prediction of the Planck Legacy analysis of the cosmic microwave background. We compare our fiducial COSEBIs (Complete Orthogonal Sets of E/B-Integrals) analysis with complementary analyses of the two-point shear correlation function and band power spectra, finding results to be in excellent agreement. We investigate the sensitivity of all three statistics to a number of measurement, astrophysical, and modelling systematics, finding our $S_8$ constraints to be robust and dominated by statistical errors. Our cosmological analysis of different divisions of the data pass the Bayesian internal consistency tests, with the exception of the second tomographic bin. As this bin encompasses low redshift galaxies, carrying insignificant levels of cosmological information, we find that our results are unchanged by the inclusion or exclusion of this sample.

• The paper details cosmic shear constraints from KiDS-1000 data using multiple statistical methods, highlighting a 3σ deviation from Planck predictions.
• It robustly compares techniques including COSEBIs, two-point shear correlations, and band power spectra to validate the cosmological findings.
• Bayesian consistency tests confirm that the derived S8 parameter is primarily limited by statistical uncertainties rather than systematic errors.

Overview of "KiDS-1000 Cosmology: Cosmic Shear Constraints and Comparison between Two-Point Statistics"

The scholarly work under discussion provides a comprehensive analysis of cosmic shear using the fourth data release of the Kilo-Degree Survey (KiDS-1000), which includes optical and near-infrared photometry. This paper marks a significant enhancement over previous cosmological analyses by effectively doubling the survey area.

The analysis conducted within a spatially flat $\Lambda$CDM framework presents the cosmic shear constraints, particularly focusing on the parameter $S_8 = \sigma_8 (\Omega_{\rm m}/0.3)^{0.5}$, which outcomes are notably a $3\sigma$ deviation from Planck Legacy analysis predictions regarding the cosmic microwave background. This manuscript also juxtaposes the fiducial Complete Orthogonal Sets of E/B Integrals (COSEBIs) analysis with techniques involving the two-point shear correlation function and band power spectra, leading to consistent results across different methodologies.

Key Numerical Findings

• The reported value $S_8 = 0.759^{+0.024}_{-0.021}$ lies in a significant $3\sigma$ tension with the values forecasted by the Planck analysis.
• The constraints derived are robust against various systematic uncertainties, signifying that statistical errors primarily bound the results.
• Bayesian internal consistency tests on the cosmological analysis of data subsets exhibit high consistency, except for some minor deviation noted in the second tomographic bin.

Methodological Approach

The researchers undertook a detailed examination of cosmic shear and its implications for cosmological parameter constraints using multiple statistical methods including COSEBIs, band power estimates, and traditional two-point correlation functions. Each technique was evaluated for its sensitivity to cosmic shear and resistance to systematic biases. These methods allowed the authors to adequately sample and analyze the relevant parameter space despite the intrinsic challenges of cosmic shear measurements including lensing-induced shape distortions.

Practical and Theoretical Implications

The reported tensions in $S_8$ between cosmic shear measurements and CMB-based predictions could imply fundamental gaps in the current cosmological model, possibly hinting at new physics or calling attention to calibration challenges inherent in these observations. The consistency across different statistical approaches reinforces the validity of the findings and suggests that the noted tension is not an artifact of a particular statistical method.

If future surveys corroborate these results, it might necessitate modifications to the dark matter and dark energy paradigms or increased scrutiny of astrophysical systematics affecting lensing measurements. The research highlights the importance of continued development in shear measurement techniques and in understanding the theoretical models used to interpret these data.

Speculation on Future Developments

The findings pave the way for future explorations in AI-driven data analysis, including the potential enhancement of statistical estimators and models used to examine cosmic shear. The scalability of AI models could significantly influence the efficiency of surveys, increasing their capacity to pinpoint and interpret astrophysical phenomena.

In conclusion, the work offers robust, statistically sound results that challenge established cosmological models, providing fertile ground for future theoretical developments and advancements in astronomical data analysis methodologies.