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

Jörg P. Dietrich, Yuanyuan Zhang, Jeeseon Song, Christopher P. Davis, Timothy A. McKay, Leon Baruah, Matthew Becker, Christophe Benoist, Michael Busha, Luiz A.N. da Costa, Jiangang Hao, Marcio A.G. Maia, Christopher J. Miller, Ricardo Ogando, A. Kathy Romer, Eduardo Rozo, Eli Rykoff, Risa Wechsler

Research output: Contribution to journalArticlepeer-review

48 Scopus citations


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.

Original languageEnglish (US)
Article numberstu1282
Pages (from-to)1713-1722
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
StatePublished - Apr 2014


  • Cosmological parameters
  • Galaxies: clusters: general
  • Gravitational lensing: weak

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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