KiDS-450: cosmological constraints from weak-lensing peak statistics – II: Inference from shear peaks using N-body simulations

Abstract

We study the statistics of peaks in a weak lensing reconstructed mass map of\nthe first 450 square degrees of the Kilo Degree Survey. The map is computed\nwith aperture masses directly applied to the shear field with an NFW-like\ncompensated filter. We compare the peak statistics in the observations with\nthat of simulations for various cosmologies to constrain the cosmological\nparameter $S_8 = \\sigma_8 \\sqrt{\\Omega_{\\rm m}/0.3}$, which probes the\n($\\Omega_{\\rm m}, \\sigma_8$) plane perpendicularly to its main degeneracy. We\nestimate $S_8=0.750\\pm0.059$, using peaks in the signal-to-noise range $0 \\leq\n{\\rm S/N} \\leq 4$, and accounting for various systematics, such as\nmultiplicative shear bias, mean redshift bias, baryon feedback, intrinsic\nalignment, and shear-position coupling. These constraints are $\\sim25\\%$\ntighter than the constraints from the high significance peaks alone ($3 \\leq\n{\\rm S/N} \\leq 4$) which typically trace single-massive halos. This\ndemonstrates the gain of information from low-S/N peaks. However we find that\nincluding ${\\rm S/N} < 0$ peaks does not add further information. Our results\nare in good agreement with the tomographic shear two-point correlation function\nmeasurement in KiDS-450. Combining shear peaks with non-tomographic\nmeasurements of the shear two-point correlation functions yields a $\\sim20\\%$\nimprovement in the uncertainty on $S_8$ compared to the shear two-point\ncorrelation functions alone, highlighting the great potential of peaks as a\ncosmological probe.\n