KiDS-Legacy: Constraining dark energy, neutrino mass, and curvature

We constrained minimally extended cosmological models with the cosmic shear analysis of the final data release from the Kilo-Degree Survey (KiDS-Legacy) in combination with external probes. Due to the consistency of the KiDS-Legacy analysis with the cosmic microwave background (CMB), we could combine these datasets reliably for the first time. Additionally, we used CMB lensing, galaxy redshift-space distortions, and baryon acoustic oscillations. We assessed, in turn, the effects of spatial curvature, varying neutrino masses, and an evolving dark energy component on cosmological constraints from KiDS-Legacy alone and from KiDS-Legacy combined with external probes. We find KiDS-Legacy to be consistent with the fiducial flat Λ-cold dark matter (ΛCDM) analysis with c 2 ∑ m ν ≤ 1.5 eV, w 0 = −1.0 ± 0.7, and w a = −1.3 −2.0 +1.9 while Ω K = 0.8 −0.17 +0.16 (1 σ bounds) with an almost equal goodness of fit. The w 0 w a CDM model is not a significant improvement over ΛCDM when cosmic shear and CMB lensing are combined, yielding a Bayes factor B = 0.07. If all probes are combined, however, B increases to 2.73, corresponding to a 2.6 σ suspiciousness tension. The constraint on S 8 = σ 8 √Ω m /0.3 is robust to opening up the parameter space for cosmic shear. Adding all external datasets to KiDS-Legacy, we find S 8 = 0.816 ± 0.006 in ΛCDM and S 8 = 0.837 ± 0.008 in w 0 w a CDM for all probes combined.