Lensing Noise in mm-wave Galaxy Cluster Surveys

TL;DR

This paper investigates how gravitational lensing by galaxy clusters affects background signals from dusty galaxies and the CMB, impacting Sunyaev-Zel'dovich surveys by altering cluster detection counts.

Contribution

It provides a detailed analysis of lensing effects on background signals and quantifies their impact on galaxy cluster detection in mm-wave surveys.

Findings

Lensing of DSFGs slightly increases cluster counts (~10%)

Lensing of CMB reduces cluster counts (~55%)

Net effect on counts is minor compared to Poisson errors

Abstract

We study the effects of gravitational lensing by galaxy clusters of the background of dusty star-forming galaxies (DSFGs) and the Cosmic Microwave Background (CMB), and examine the implications for Sunyaev-Zel'dovich-based (SZ) galaxy cluster surveys. At the locations of galaxy clusters, gravitational lensing modifies the probability distribution of the background flux of the DSFGs as well as the CMB. We find that, in the case of a single-frequency 150 GHz survey, lensing of DSFGs leads to both a slight increase (~10%) in detected cluster number counts (due to a ~ 50% increase in the variance of the DSFG background, and hence an increased Eddington bias), as well as to a rare (occurring in ~2% of clusters) "filling-in" of SZ cluster signals by bright strongly lensed background sources. Lensing of the CMB leads to a ~55% reduction in CMB power at the location of massive galaxy clusters in a spatially-matched single-frequency filter, leading to a net decrease in detected cluster number counts. We find that the increase in DSFG power and decrease in CMB power due to lensing at cluster locations largely cancel, such that the net effect on cluster number counts for current SZ surveys is sub-dominant to Poisson errors.