KiDS-1000 Cosmology: Multi-probe weak gravitational lensing and spectroscopic galaxy clustering constraints (2007.15632v2)

Abstract: We present a joint cosmological analysis of weak gravitational lensing observations from the Kilo-Degree Survey (KiDS-1000), with redshift-space galaxy clustering observations from the Baryon Oscillation Spectroscopic Survey (BOSS), and galaxy-galaxy lensing observations from the overlap between KiDS-1000, BOSS and the spectroscopic 2-degree Field Lensing Survey (2dFLenS). This combination of large-scale structure probes breaks the degeneracies between cosmological parameters for individual observables, resulting in a constraint on the structure growth parameter $S_8=\sigma_8 \sqrt{\Omega_{\rm m}/0.3} = 0.766^{+0.020}_{-0.014}$, that has the same overall precision as that reported by the full-sky cosmic microwave background observations from Planck. The recovered $S_8$ amplitude is low, however, by $8.3 \pm 2.6$ % relative to Planck. This result builds from a series of KiDS-1000 analyses where we validate our methodology with variable depth mock galaxy surveys, our lensing calibration with image simulations and null-tests, and our optical-to-near-infrared redshift calibration with multi-band mock catalogues and a spectroscopic-photometric clustering analysis. The systematic uncertainties identified by these analyses are folded through as nuisance parameters in our cosmological analysis. Inspecting the offset between the marginalised posterior distributions, we find that the $S_8$-difference with Planck is driven by a tension in the matter fluctuation amplitude parameter, $\sigma_8$. We quantify the level of agreement between the CMB and our large-scale structure constraints using a series of different metrics, finding differences with a significance ranging between $\sim! 3\,\sigma$, when considering the offset in $S_{8}$, and $\sim! 2\,\sigma$, when considering the full multi-dimensional parameter space.

• The paper combines KiDS-1000 weak lensing and BOSS clustering to constrain the structure growth parameter S8 to 0.766±0.020.
• It identifies a 2–3σ tension between low-redshift large-scale structure measurements and high-redshift CMB constraints from Planck.
• The analysis employs advanced Bayesian inference with rigorous systematics checks, setting a benchmark for future multi-probe cosmological surveys.

Overview of the KiDS-1000 Multi-Probe Weak Gravitational Lensing and Spectroscopic Galaxy Clustering Analysis

The paper "KiDS-1000 Cosmology: Multi-probe weak gravitational lensing and spectroscopic galaxy clustering constraints" presents a comprehensive cosmological analysis involving weak gravitational lensing data from the Kilo-Degree Survey (KiDS-1000), redshift-space galaxy clustering data from the Baryon Oscillation Spectroscopic Survey (BOSS), and galaxy-galaxy lensing data from the overlapping regions of KiDS-1000, BOSS, and the 2-degree Field Lensing Survey (2dFLenS). The integration of these datasets offers a robust means to break the degeneracies inherent in cosmological parameters when considering observations individually, thereby enhancing the precision of cosmological constraints.

Key Findings

1. Constraint on Structure Growth Parameter: The combination of KiDS-1000 and BOSS data constrains the structure growth parameter $S_8 = \sigma_8 \sqrt{\Omega_{\rm m}/0.3}$ to be $0.766^{+0.020}$. This finding matches the precision of full-sky cosmic microwave background (CMB) observations by the Planck survey. However, the recovered $S_8$ value is lower than Planck's expectation by about 8.3%.
2. Tension with Planck Data: The paper identifies noticeable tension between the low-redshift large-scale structure observations and the high-redshift CMB constraints from Planck. The significance of the $S_8$ discrepancy ranges between $2\sigma$ to $3\sigma$, depending on the full multi-dimensional parameter space considered.
3. Methodological Robustness: The paper presents a series of systematics checks and validation tests, incorporating synthetic galaxy catalogues and image simulations. These efforts ensure the reliability of catalog-level blinding and systematic error assessments.
4. Non-linear Galaxy Bias: The analysis adopts a detailed non-linear galaxy bias model, derived from renormalized perturbation theory, extending beyond the linear models commonly used. Constraints on the linear galaxy bias $b_1$ are refined by the inclusion of lensing data, which, when combined with clustering metrics, provide narrower bounds.
5. Parameter Recovery Techniques: The work emphasizes advanced Bayesian inference methodologies, specifically employing the KiDS Cosmology Analysis Pipeline (KCAP) and the CosmoSIS framework. The analyses account for potential implicit priors and adopt direct sampling in $S_8$, minimizing subjective influences on parameter estimates.

Implications and Future Directions

• Resource for Future Surveys: The findings and methodologies detailed in this paper establish a benchmark for future cosmological surveys like ESA's Euclid and the Vera C. Rubin Observatory. Both are anticipated to further refine analysis techniques and potentially resolve current discrepancies with Planck data.
• Enhanced Multi-Probe Analyses: The paper demonstrates the value of multi-probe analyses in reducing parameter space degeneracies. As datasets continue to improve in scope and precision, such comprehensive approaches will become increasingly important in cosmology.
• Potential for New Physics: Given the consistent discrepancy in $S_8$ values, the findings could suggest the necessity for models extending beyond the flat $\Lambda$CDM framework. These would account for new physics potentially influencing cosmic structure growth.

The KiDS-1000 analysis exemplifies an iterative step towards precise cosmological parameter determination using a confluence of observational probes. As the field progresses, alignment between low-redshift and CMB observations will be crucial in elucidating the nuances of cosmic evolution and the fundamental forces shaping the universe.