Weak Lensing Peak Finding: Estimators, Filters, and Biases

TL;DR

This paper examines how different shear estimators and filters affect the detection and interpretation of weak lensing peaks, highlighting biases and systematic effects that influence peak counts and their statistical significance.

Contribution

It compares globally- and locally-normalized shear estimators, analyzing their responses to biases and how estimator-filter combinations impact peak detection accuracy.

Findings

Estimator choice affects peak counts significantly.

Lensing bias can increase peak signal-to-noise by 1-2.

Suboptimal estimator-filter pairs can suppress high peaks by orders of magnitude.

Abstract

Large catalogs of shear-selected peaks have recently become a reality. In order to properly interpret the abundance and properties of these peaks, it is necessary to take into account the effects of the clustering of source galaxies, among themselves and with the lens. In addition, the preferred selection of lensed galaxies in a flux- and size-limited sample leads to fluctuations in the apparent source density which correlate with the lensing field (lensing bias). In this paper, we investigate these issues for two different choices of shear estimators which are commonly in use today: globally-normalized and locally-normalized estimators. While in principle equivalent, in practice these estimators respond differently to systematic effects such as lensing bias and cluster member dilution. Furthermore, we find that which estimator is statistically superior depends on the specific shape of the filter employed for peak finding; suboptimal choices of the estimator+filter combination can result in a suppression of the number of high peaks by orders of magnitude. Lensing bias generally acts to increase the signal-to-noise \nu of shear peaks; for high peaks the boost can be as large as \Delta \nu ~ 1-2. Due to the steepness of the peak abundance function, these boosts can result in a significant increase in the abundance of shear peaks. A companion paper (Rozo et al., 2010) investigates these same issues within the context of stacked weak lensing mass estimates.