A New Measure for Weak‐Lensing Flexion

We present weak-lensing mass measurements of 50 X-ray luminous galaxy clusters at 0.15 z 0.3, based on uniform high quality observations with Suprime-Cam mounted on the 8.2-m Subaru telescope. We pay close attention to possible systematic biases, aiming to control them at the ∼ < 4 per cent level. The dominant source of systematic bias in weak-lensing measurements of the mass of individual galaxy clusters is contamination of background galaxy catalogues by faint cluster and foreground galaxies. We extend our conservative method for selecting background galaxies with (V − i ′ ) colours redder than the red sequence of cluster members to use a colour-cut that depends on cluster-centric radius. This allows us to define background galaxy samples that suffer 1 per cent contamination, and comprise 13 galaxies per square arcminute. Thanks to the purity of our background galaxy catalogue, the largest systematic that we identify in our analysis is a shape measurement bias of 3 per cent, that we measure using simulations that probe weak shears upto g = 0.3. Our individual cluster mass and concentration measurements are in excellent agreement with predictions of the mass-concentration relation. Equally, our stacked shear profile is in excellent agreement with the Navarro Frenk and White profile. Our new LoCuSS mass measurements are consistent with the CCCP and CLASH surveys, and in tension with the Weighing the Giants at ∼ 1 − 2σ significance. Overall, the consensus at z 0.3 that is emerging from these complementary surveys represents important progress for cluster mass calibration, and augurs well for cluster cosmology.

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“…Okura, Umetsu & Futamase 2007). Higher order effects are negligible on the scale that we measure and fit the shear profile of clusters.…”

Section: Shape Measurement Testsmentioning

confidence: 95%

LoCuSS: weak-lensing mass calibration of galaxy clusters

Okabe

Smith

2016

Mon. Not. R. Astron. Soc.

153

179

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“…Secondary lensing effects have been considered in the past, and generically go under the name 'flexion', describing classic arc shaped images, though there are other effects from secondary lensing [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. In these works, the flexion has been derived by Taylor expanding the amplification matrix (which is usually the linearisation of the Jacobi map about an FLRW background) across the image plane.…”

Section: Introduction and Overviewmentioning

confidence: 99%

The general theory of secondary weak gravitational lensing

Clarkson

2015

J. Cosmol. Astropart. Phys.

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Weak gravitational lensing is normally assumed to have only two principle effects: a magnification of a source and a distortion of the sources shape in the form of a shear. However, further distortions are actually present owing to changes in the gravitational field across the scale of the ray bundle of light propagating to us, resulting in the familiar arcs in lensed images. This is normally called the flexion, and is approximated by Taylor expanding the shear and magnification across the image plane. However, the physical origin of this effect arises from higher-order corrections in the geodesic deviation equation governing the gravitational force between neighbouring geodesics -so involves derivatives of the Riemann tensor. We show that integrating the second-order geodesic deviation equation results in a 'Hessian map' for gravitational lensing, which is a higher-order addition to the Jacobi map. We derive the general form of the Hessian map in an arbitrary spacetime paying particular attention to the separate effects of local Ricci versus non-local Weyl curvature. We then specialise to the case of a perturbed FLRW model, and give the general form of the Hessian for the first time. This has a host of new contributions which could in principle be used as tests for modified gravity.

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“…Different techniques were developed to measure flexion (Irwin & Shmakova 2006;Okura et al 2007;Massey et al 2007;Schneider & Er 2008). It was noted that flexion can contribute to studies of the dark matter halos in galaxies and clusters, especially for the detection of mass substructure (Bacon et al 2010;Er et al 2010).…”

Section: Introductionmentioning

confidence: 99%

Estimate of dark halo ellipticity by lensing flexion

Schneider

2011

A&A

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Aims. The predictions of the ellipticity of dark matter halos from models of structure formation are notoriously difficult to test with observations. A direct measurement would give important constraints on the formation of galaxies, and its effect on the dark matter distribution in their halos. Here we show that galaxy-galaxy flexion provides a direct and potentially powerful method for determining the ellipticity of (an ensemble of) elliptical lenses. Methods. We decompose the spin-1 flexion into a radial and a tangential component. Using the ratio of tangential-to-radial flexion, which is independent of the radial mass profile, the mass ellipticity can be estimated.Results. An estimator for the ellipticity of the mass distribution is derived and tested with simulations. We show that the estimator is slightly biased. We quantify this bias, and provide a method to reduce it. Furthermore, a parametric fitting of the flexion ratio and orientation provides another estimate for the dark halo ellipticity, which is more accurate for individual lenses. Overall, galaxy-galaxy flexion appears as a powerful tool for constraining the ellipticity of mass distributions.

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A New Measure for Weak‐Lensing Flexion

Cited by 77 publications

References 13 publications

LoCuSS: weak-lensing mass calibration of galaxy clusters

LoCuSS: weak-lensing mass calibration of galaxy clusters

The general theory of secondary weak gravitational lensing

Estimate of dark halo ellipticity by lensing flexion

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