Halo ellipticity of GAMA galaxy groups from KiDS weak lensing

Edo van Uitert*, Henk Hoekstra, Benjamin Joachimi, Peter Schneider, Joss Bland-Hawthorn, Ami Choi, Thomas Erben, Catherine Heymans, Hendrik Hildebrandt, Andrew M. Hopkins, Dominik Klaes, Konrad Kuijken, Reiko Nakajima, Nicola R. Napolitano, Tim Schrabback, Edwin Valentijn, Massimo Viola

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

28 Citations (Scopus)

Abstract

We constrain the average halo ellipticity of ˜2600 galaxy groups from the Galaxy And Mass Assembly (GAMA) survey, using the weak gravitational lensing signal measured from the overlapping Kilo Degree Survey (KiDS). To do so, we quantify the azimuthal dependence of the stacked lensing signal around seven different proxies for the orientation of the dark matter distribution, as it is a priori unknown which one traces the orientation best. On small scales, the major axis of the brightest group/cluster member (BCG) provides the best proxy, leading to a clear detection of an anisotropic signal. In order to relate that to a halo ellipticity, we have to adopt a model density profile. We derive new expressions for the quadrupole moments of the shear field given an elliptical model surface mass density profile. Modelling the signal with an elliptical Navarro-Frenk-White profile on scales R < 250 kpc, and assuming that the BCG is perfectly aligned with the dark matter, we find an average halo ellipticity of εh = 0.38 ± 0.12, in fair agreement with results from cold dark matter only simulations. On larger scales, the lensing signal around the BCGs becomes isotropic and the distribution of group satellites provides a better proxy for the halo's orientation instead, leading to a 3σ-4σ detection of a non-zero halo ellipticity at 250 < R < 750 kpc. Our results suggest that the distribution of stars enclosed within a certain radius forms a good proxy for the orientation of the dark matter within that radius, which has also been observed in hydrodynamical simulations.

Original languageEnglish
Pages (from-to)4131-4149
Number of pages19
JournalMonthly Notices of the Royal Astronomical Society
Volume467
Issue number4
DOIs
Publication statusPublished - 1 Jun 2017
Externally publishedYes

Keywords

  • data analysis - methods
  • general - galaxies
  • gravitational lensing
  • groups
  • haloes
  • statistical - galaxies
  • weak - methods

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