Orientation bias of optically selected galaxy clusters and its impact on stacked weak-lensing analyses

Romer, Kathy and The DES Collaboration, et al (2014) Orientation bias of optically selected galaxy clusters and its impact on stacked weak-lensing analyses. Monthly Notices of the Royal Astronomical Society, 443 (2). pp. 1713-1722. ISSN 0035-8711

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Abstract

Weak-lensing measurements of the averaged shear profiles of galaxy clusters binned by some proxy for cluster mass are commonly converted to cluster mass estimates under the assumption that these cluster stacks have spherical symmetry. In this paper, we test whether this assumption holds for optically selected clusters binned by estimated optical richness. Using mock catalogues created from N-body simulations populated realistically with galaxies, we ran a suite of optical cluster finders and estimated their optical richness. We binned galaxy clusters by true cluster mass and estimated optical richness and measure the ellipticity of these stacks. We find that the processes of optical cluster selection and richness estimation are biased, leading to stacked structures that are elongated along the line of sight. We show that weak-lensing alone cannot measure the size of this orientation bias. Weak-lensing masses of stacked optically selected clusters are overestimated by up to 3-6 per cent when clusters can be uniquely associated with haloes. This effect is large enough to lead to significant biases in the cosmological parameters derived from large surveys like the Dark Energy Survey, if not calibrated via simulations or fitted simultaneously. This bias probably also contributes to the observed discrepancy between the observed and predicted Sunyaev-Zel'dovich signal of optically selected clusters.

Item Type: Article
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Subjects: Q Science > QB Astronomy
Depositing User: Richard Chambers
Date Deposited: 28 Jun 2016 12:25
Last Modified: 23 Mar 2017 12:41
URI: http://sro.sussex.ac.uk/id/eprint/61758

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Project NameSussex Project NumberFunderFunder Ref
Astronomy rolling grantG0278STFC-SCIENCE AND TECHNOLOGY FACILITIES COUNCILST/I000976/1
2012 Doctoral Training Grant - Quota Studentships (STFC)G0939STFC-SCIENCE AND TECHNOLOGY FACILITIES COUNCILST/K502364/1