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Martinet, Nicolas; Schneider, Peter; Hildebrandt, Hendrik; Shan, HuanYuan; Asgari, Marika; Dietrich, Jörg P.; Harnois-Deraps, Joachim; Erben, Thomas; Grado, Aniello; Heymans, Catherine; Hoekstra, Henk; Klaes, Dominik; Kuijken, Konrad; Merten, Julian; Nakajima, Reiko (2018): KiDS-450: cosmological constraints from weak-lensing peak statistics - II: Inference from shear peaks using N-body simulations. In: Monthly Notices of the Royal Astronomical Society, Vol. 474, No. 1: pp. 712-730
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Abstract

We study the statistics of peaks in a weak-lensing reconstructed mass map of the first 450 deg(2) of the Kilo Degree Survey (KiDS-450). The map is computed with aperture masses directly applied to the shear field with an NFW-like compensated filter. We compare the peak statistics in the observations with that of simulations for various cosmologies to constrain the cosmological parameter S-8 = sigma(8) root Omega(m)/0.3, which probes the (Omega(m), sigma(8)) plane perpendicularly to its main degeneracy. We estimate S-8 = 0.750 +/- 0.059, using peaks in the signal-to-noise range 0 <= S/N <= 4, and accounting for various systematics, such as multiplicative shear bias, mean redshift bias, baryon feedback, intrinsic alignment, and shear-position coupling. These constraints are similar to 25 per cent tighter than the constraints from the high significance peaks alone (3 <= S/N <= 4) which typically trace single-massive haloes. This demonstrates the gain of information from low-S/N peaks. However, we find that including S/N < 0 peaks does not add further information. Our results are in good agreement with the tomographic shear two-point correlation function measurement in KiDS-450. Combining shear peaks with non-tomographic measurements of the shear two-point correlation functions yields a similar to 20 per cent improvement in the uncertainty on S-8 compared to the shear two-point correlation functions alone, highlighting the great potential of peaks as a cosmological probe.