Mass Bias of Weak Lensing Shear-selected Galaxy Cluster Samples

TL;DR

This paper quantifies the significant mass bias in weak lensing shear-selected galaxy cluster samples, showing it is mainly due to noise-induced up-scattering of low-mass objects, which impacts cosmological and astrophysical studies.

Contribution

It provides a detailed analysis of the mass bias in shear-selected clusters using simulations, and models its dependence on various parameters, aiding future cosmological applications.

Findings

Weak lensing masses are biased high by ~55% on average.

Mass bias correlates with cluster redshift, true mass, and S/N threshold.

Bias can be modeled and explained in the context of previous observational deviations.

Abstract

We estimate the bias on weak lensing mass measurements of shear-selected galaxy cluster samples. The mass bias is expected to be significant because constructions of cluster samples from peaks in weak lensing mass maps and measurements of cluster masses from their tangential shear profiles share the same noise. We quantify this mass bias from large sets of mock cluster samples with analytical density profiles and realistic large-scale structure noise from ray-tracing simulations. We find that, even for peaks with signal-to-noise ratio larger than $4.0$ in weak lensing mass maps constructed in a deep survey with a high source galaxy number density of $30~\mathrm{arcmin}^{-2}$, derived weak lensing masses for these shear-selected clusters are still biased high by $\sim55\%$ on average. Such a large bias mainly originates from up-scattered low mass objects, which is an inevitable consequence of selecting clusters with a noisy observable directly linked to the mass measurement. We also investigate the dependence of the mass bias on different physical and observational parameters, finding that the mass bias strongly correlates with cluster redshifts, true halo masses, and selection signal-to-noise thresholds, but having moderate dependence on observed weak lensing masses and survey depths. This bias, albeit considerable, can still be modeled accurately in statistical studies of shear-selected clusters as the intrinsic scatter around the mean bias is found to be reasonable in size. We demonstrate that such a bias can explain the deviation in X-ray properties previously found on a shear-selected cluster sample. Our result will be useful for turning large samples of shear-selected clusters available in future surveys into potential probes of cosmology and cluster astrophysics.