KiDS-1000 cosmology: Combined second- and third-order shear statistics

Abstract

This paper performs the first cosmological parameter analysis of the KiDS-1000 data with second- and third-order shear statistics. This work builds on a series of papers that describe the roadmap to third-order shear statistics. We derive and test a combined model of the second-order shear statistic, namely the COSEBIs and the third-order aperture mass statistics $\langle M_\mathrm{ap}^3\rangle$ in a tomographic set-up. We validate our pipeline with $N$-body simulations that mock the fourth Kilo Degree survey data release. To model the second- and third-order statistics, we use the latest version of \textsc{HMcode2020} for the power spectrum and \textsc{BiHalofit} for the bispectrum. Furthermore, we use an analytic description to model intrinsic alignments and hydro-dynamical simulations to model the effect of baryonic feedback processes. Lastly, we decreased the dimension of the data vector significantly by considering for the $\langle M_\mathrm{ap}^3\rangle$ part of the data vector only equal smoothing radii, making a data analysis of the fourth Kilo Degree survey data release using a combined analysis of COSEBIs third-order shear statistic possible. We first validate the accuracy of our modelling by analysing a noise-free mock data vector assuming the KiDS-1000 error budget, finding a shift in the maximum-a-posterior of the matter density parameter $ΔΩ_m< 0.02\, σ_{Ω_m}$ and of the structure growth parameter $ΔS_8 < 0.05\, σ_{S_8}$. Lastly, we performed the first KiDS-1000 cosmological analysis using a combined analysis of second- and third-order shear statistics, where we constrained $Ω_m=0.248^{+0.062}_{-0.055}$ and $S_8=σ_8\sqrt{Ω_m/0.3}=0.772\pm0.022$. The geometric average on the errors of $Ω_\mathrm{m}$ and $S_8$ of the combined statistics increased compared to the second-order statistic by 2.2.