KiDS-Legacy: Consistency of cosmic shear measurements and joint cosmological constraints with external probes

Abstract: We present a cosmic shear consistency analysis of the final data release from the Kilo-Degree Survey (KiDS-Legacy). By adopting three tiers of consistency metrics, we compare cosmological constraints between subsets of the KiDS-Legacy dataset split by redshift, angular scale, galaxy colour and spatial region. We also review a range of two-point cosmic shear statistics. With the data passing all our consistency metric tests, we demonstrate that KiDS-Legacy is the most internally consistent KiDS catalogue to date. In a joint cosmological analysis of KiDS-Legacy and DES Y3 cosmic shear, combined with data from the Pantheon+ Type Ia supernovae compilation and baryon acoustic oscillations from DESI Y1, we find constraints consistent with Planck measurements of the cosmic microwave background with $S_8\equiv \sigma_8\sqrt{\Omega_{\rm m}/0.3} = 0.814^{+0.011}_{-0.012}$ and $\sigma_8 = 0.802^{+0.022}_{-0.018}$.

Analysis of KiDS-Legacy Consistency with External Cosmological Constraints

The paper presents an in-depth analysis of cosmic shear measurements from the final data release of the Kilo-Degree Survey (KiDS-Legacy) and evaluates their internal consistency and alignment with external cosmological probes. This comprehensive study uses a three-tiered approach to scrutinize the dataset's consistency across various splits, enabling robust statistical checks against systematic biases and enhancing the credibility of its cosmological inferences.

Methodology Overview

The authors employed three-tier consistency metrics to test the internal robustness of the KiDS-Legacy dataset. The analysis was conducted by dividing the dataset into numerous subsets based on redshift, angular scale, galaxy color, and spatial region. Additionally, comparisons were drawn with findings from other prominent cosmic shear datasets such as the @@@@2@@@@ (DES) Y3 and various external datasets like the Pantheon+ Type Ia supernovae compilation and baryon acoustic oscillations (BAO) from @@@@3@@@@ Y1.

1. Tier 1 - Evidence-Based Metrics: Bayesian evidence comparisons provided a quantitative measure of whether the data subsets prefer the same cosmological model. The paper details how, for most of the data splits, there was no substantial evidence to favor a split model over a unified one, indicating robust internal consistency.

1. Tier 2 - Multi-Dimensional Parameter Metrics: By examining potential shifts in key cosmological parameters (e.g., $\Omega_m$, $S_8$), the analysis confirms an agreement between the parameter spaces of the data subsets. The shifts observed were mostly within acceptable ranges for statistical noise, suggesting that no parameter showed significant systematic deviation across data splits.
2. Tier 3 - Posterior Predictive Distribution Metrics: The use of posterior predictive distributions enabled direct compatibility assessments between observed data and model predictions. This tier confirmed that the observed cosmic shear data fits well within the model predictions, further supporting the internal consistency of the dataset.

Results and Implications

An essential finding of the study was the consistency of KiDS-Legacy cosmic shear measurements with those from DES Y3, DESI Y1 BAO, and Pantheon+ datasets. The joint analysis reported $S_8=0.814^{+0.011}_{-0.012}$ and $\sigma_8=0.802^{+0.022}_{-0.018}$, showing excellent alignment with Planck CMB constraints and removing the previously noted $S_8$ tension observed in former analyses.

The paper also emphasizes the potential issues that could surface when different summary statistics are employed for cosmic shear analysis, warranting caution and thorough cross-checking to avoid systematic biases in cosmological conclusions.

Future Directions

The data consistency demonstrated by KiDS-Legacy paves the way for its use in future cosmological analyses, potentially including testing extended cosmological models beyond $\Lambda$CDM. Moreover, the methodologies applied here set a precedent for rigor in upcoming analyses from next-generation surveys such as those conducted by the Vera C. Rubin Observatory and the Euclid satellite.

This paper exemplifies how methodical internal and external consistency checks can enhance the reliability of derived cosmological constraints, thereby strengthening the scientific community's confidence in using cosmic shear as a robust cosmological probe.