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

TL;DR

This work validates the internal consistency of the KiDS-Legacy cosmic shear data using a three-tier framework and demonstrates its compatibility with external probes (DESI Y1 BAO, Pantheon+, eBOSS, Planck) in joint cosmological analyses. By comparing six tomographic redshift bins, auto- and cross-correlations, and multiple two-point statistics (COSEBIs, band powers, 2PCFs), the study shows the dataset is internally coherent and capable of yielding robust cosmological constraints. The joint analyses tighten constraints on S8 and Ωm and align with Planck CMB results, effectively alleviating the previous S8 tension. The results also highlight intrinsic alignments as red galaxies exhibit strong IA while blue galaxies show negligible alignment, reinforcing the need for colour-dependent IA modeling. Overall, KiDS-Legacy delivers high-precision, self-consistent cosmology that integrates smoothly with external datasets, providing a blueprint for future surveys.

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 $S_8\equiv σ_8\sqrt{Ω_{\rm m}/0.3} = 0.814^{+0.011}_{-0.012}$ and $σ_8 = 0.802^{+0.022}_{-0.018}$.

Figures (16)

• Figure 1: Posterior distribution of the two instances of cosmological parameters in a split by redshift bin for COSEBIs. The yellow contours show the posterior of parameters modelling one specific redshift bin and its cross-correlation with the other bins, while the red contours show the posterior distribution of the parameters modelling the auto- and cross-correlation signal of the remaining redshift bins. The dashed contours show the fiducial constraints for reference. The final panel presents the posterior distribution in a split between auto-correlations of all redshift bins and their cross-correlations. When running the chains, both regimes are linked through the cross-covariance between redshift bins. The inner and outer contours of the marginalised posteriors correspond to the 68% and 95% credible intervals, respectively.
• Figure 2: Posterior distribution of the two instances of cosmological parameters in a split by scale for 2PCFs (left), band powers (middle), and COSEBIs (right) in comparison to the fiducial analysis with each summary statistic, illustrated by the black dashed lines. The inner and outer contours of the marginalised posteriors correspond to the 68% and 95% credible intervals, respectively.
• Figure 3: COSEBIs E-mode measurements and their best-fitting model for a split cosmological analysis of the North-South split catalogue. The green and purple data points show the measurements of the KiDS-North and KiDS-South sample, respectively. The best-fitting theoretical predictions are given by the solid lines, and the $1\sigma$ interval of the TPDs are illustrated by the shaded regions. Each panel represents auto- or cross-correlation between tomographic bins. For visualisation purposes, we display the discrete $n$ modes with an offset on the x-axis.We note that the E-mode signals are highly correlated within a tomographic bin and advise against a so-called ""*$\chi$-by-eye.
• Figure 4: Posterior distribution of parameter duplicates in the $\Omega_{\rm m}-S_8$ plane for catalogue-level splits for COSEBIs. Left panel: North-South split. Middle panel: Red-blue split defined via a cut on the spectral type of $T_{\rm B}=3.0$. Right panel: Red-blue split defined via a cut on the spectral type of $T_{\rm B}=1.9$. For reference, the black dashed contours show constraints from the analysis with a single set of parameters modelling both data subsets. The inner and outer contours of the marginalised posteriors correspond to the 68% and 95% credible intervals, respectively.
• Figure 5: COSEBIs E-mode measurements and their best-fitting model for a split cosmological analysis of the red-blue split catalogue, defined via a cut on the spectral type $T_{\rm B}=3.0$. The red and blue data points show the measurements of the red and blue sample, respectively. The best-fitting theoretical predictions are given by the solid lines, and the $1\sigma$ interval of the TPDs are illustrated by the shaded regions. Each panel represents auto- or cross-correlation between tomographic bins, as indicated by the label in the top right corner. For visualisation purposes, we display the discrete $n$ modes with an offset on the x-axis. We note that the E-mode signals are highly correlated within a tomographic bin and advise against a so-called ""*$\chi$-by-eye.