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

TL;DR

This study combines KiDS-Legacy cosmic shear data with external probes to constrain cosmological models, finding consistency with flat $ ext{Lambda}$CDM and exploring effects of curvature, neutrino mass, and dark energy evolution.

Contribution

First reliable combination of KiDS-Legacy data with multiple external probes to constrain extended cosmological models including curvature and evolving dark energy.

Findings

KiDS-Legacy data consistent with flat $ ext{Lambda}$CDM with $ ext{sum } m_ u extless 1.5$ eV.

Adding all probes yields $S_8=0.837 ext{ with } ext{w}_0 ext{w}_a$CDM, indicating robust constraints.

Bayes factor analysis shows no significant preference for extended models over $ ext{Lambda}$CDM.

Abstract

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 $\Lambda$-cold dark matter ($\Lambda$CDM) analysis with $c^2 \sum m_\nu\leq 1.5\,$eV, $w_0 = -1.0\pm 0.7$, and $w_a = -1.3^{+1.9}_{-2.0}$ while $\Omega_K = 0.08^{+0.16}_{-0.17}$ (1$\sigma$ bounds) with an almost equal goodness of fit. The $w_0w_a$CDM model is not a significant improvement over $\Lambda$CDM 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 $2.6\sigma$ suspiciousness tension. The constraint on $S_8 = \sigma_8\sqrt{\Omega_\mathrm{m}/0.3}$ is robust to opening up the parameter space for cosmic shear. Adding all external datasets to KiDS-Legacy, we find $S_8 = 0.816 \pm 0.006$ in $\Lambda$CDM and $S_8 = 0.837 \pm 0.008$ in $w_0 w_a$CDM for all probes combined.