Ellipticity of brightest cluster galaxies as tracer of halo orientation and weak-lensing mass bias

Ricardo Herbonnet, Anja von der Linden, Steven W. Allen, Adam B. Mantz, Pranati Modumudi, R. Glenn Morris, Patrick L. Kelly

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


Weak-lensing measurements of the masses of galaxy clusters are commonly based on the assumption of spherically symmetric density profiles. Yet, the cold dark matter model predicts the shapes of dark matter haloes to be triaxial. Halo triaxiality, and the orientation of the major axis with respect to the line of sight, are expected to be the leading cause of intrinsic scatter in weak-lensing mass measurements. The shape of central cluster galaxies (brightest cluster galaxies; BCGs) is expected to follow the shape of the dark matter halo. Here we investigate the use of BCG ellipticity as predictor of the weak-lensing mass bias in individual clusters compared to the mean. Using weak-lensing masses M500WL from the Weighing the Giants project, and M500 derived from gas masses as low-scatter mass proxy, we find that, on average, the lensing masses of clusters with the roundest/most elliptical 25 per cent of BCGs are biased ∼20 per cent high/low compared to the average, as qualitatively predicted by the cold dark matter model. For cluster cosmology projects utilizing weak-lensing mass estimates, the shape of the BCG can thus contribute useful information on the effect of orientation bias in weak-lensing mass estimates as well as on cluster selection bias.

Original languageEnglish (US)
Pages (from-to)4889-4897
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - Dec 1 2019

Bibliographical note

Funding Information:
RH and AvdL are supported by the US Department of Energy under award DE-SC0018053. PM acknowledges support of the Simons Summer Research Program at Stony Brook. SWA, ABM, and RGM acknowledge support from the U.S. Department of Energy under contract number DE-AC02-76SF00515, and from the National Aeronautics and Space Administration (NASA) through Chandra Award Number GO8-19101A, issued by the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics and Space Administration under contract NAS8-03060 and from the National Aeronautics and Space Administration under Grant Number NNX15AE12G issued through the ROSES 2014 Astrophysics Data Analysis Program.

Publisher Copyright:
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society


  • Cosmology: observations
  • Galaxies: groups: general
  • Methods: data analysis


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