KiDS-450: cosmological constraints from weak lensing peak statistics – I. Inference from analytical prediction of high signal-to-noise ratio convergence peaks

Abstract

This paper is the first of a series of papers constraining cosmological\nparameters with weak lensing peak statistics using $\\sim 450~\\rm deg^2$ of\nimaging data from the Kilo Degree Survey (KiDS-450). We measure high\nsignal-to-noise ratio (SNR: $\\nu$) weak lensing convergence peaks in the range\nof $3<\\nu<5$, and employ theoretical models to derive expected values. These\nmodels are validated using a suite of simulations. We take into account two\nmajor systematic effects, the boost factor and the effect of baryons on the\nmass-concentration relation of dark matter haloes. In addition, we investigate\nthe impacts of other potential astrophysical systematics including the\nprojection effects of large scale structures, intrinsic galaxy alignments, as\nwell as residual measurement uncertainties in the shear and redshift\ncalibration. Assuming a flat $\\Lambda$CDM model, we find constraints for\n$S_{\\rm 8}=\\sigma_{\\rm 8}(\\Omega_{\\rm m}/0.3)^{0.5}=0.746^{+0.046}_{-0.107}$\naccording to the degeneracy direction of the cosmic shear analysis and\n$\\Sigma_{\\rm 8}=\\sigma_{\\rm 8}(\\Omega_{\\rm\nm}/0.3)^{0.38}=0.696^{+0.048}_{-0.050}$ based on the derived degeneracy\ndirection of our high-SNR peak statistics. The difference between the power\nindex of $S_{\\rm 8}$ and in $\\Sigma_{\\rm 8}$ indicates that combining the two\nprobes has the potential to break the degeneracy in $\\sigma_{\\rm 8}$ and\n$\\Omega_{\\rm m}$. Our results are consistent with the cosmic shear tomographic\ncorrelation analysis of the same dataset and $\\sim 2\\sigma$ lower than the\nPlanck 2016 results.\n