KiDS-1000 Cosmology: Multi-probe weak gravitational lensing and spectroscopic galaxy clustering constraints

We present a joint cosmological analysis of weak gravitational lensing observations from the Kilo-Degree Survey (KiDS-1000), withredshift-space galaxy clustering observations from the Baryon Oscillation Spectroscopic Survey (BOSS) and galaxy-galaxy lensingobservations from the overlap between KiDS-1000, BOSS, and the spectroscopic 2-degree Field Lensing Survey (2dFLenS). Thiscombination of large-scale structure probes breaks the degeneracies between cosmological parameters for individual observables,resulting in a constraint on the structure growth parameterS8=σ8√Ωm/0.3=0.766+0.020−0.014, which has the same overall precision asthat reported by the full-sky cosmic microwave background observations fromPlanck. The recoveredS8amplitude is low, however,by8.3±2.6%relative toPlanck. This result builds from a series of KiDS-1000 analyses where we validate our methodology withvariable depth mock galaxy surveys, our lensing calibration with image simulations and null-tests, and our optical-to-near-infraredredshift calibration with multi-band mock catalogues and a spectroscopic-photometric clustering analysis. The systematic uncertain-ties identified by these analyses are folded through as nuisance parameters in our cosmological analysis. Inspecting the offset betweenthe marginalised posterior distributions, we find that theS8-difference withPlanckis driven by a tension in the matter fluctuationamplitude parameter,σ8. We quantify the level of agreement between the cosmic microwave background and our large-scale structureconstraints using a series of different metrics, finding differences with a significance ranging between∼3σ, when considering theoffset inS8, and∼2σ, when considering the full multi-dimensional parameter space