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Numerical simulations of weak lensing measurements

Bacon, David. J. and Refregier, Alexandre and Clowe, Douglas and Ellis, Richard S. (2001) Numerical simulations of weak lensing measurements. Monthly Notices of the Royal Astronomical Society, 325 (3). pp. 1065-1074. ISSN 0035-8711. doi:10.1046/j.1365-8711.2001.04507.x.

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Weak gravitational lensing induces distortions on the images of background galaxies, and thus provides a direct measure of mass fluctuations in the Universe. The distortion signature from large-scale structure has recently been detected by several groups for the first time, opening promising prospects for the near future. Since the distortions induced by lensing on the images of background galaxies are only of the order of a few per cent, a reliable measurement demands very accurate galaxy shape estimation and a careful treatment of systematic effects. Here, we present a study of a shear measurement method using detailed simulations of artificial images. The images are produced using realizations of a galaxy ensemble drawn from the Hubble Space Telescope Groth strip. We consider realistic observational effects including atmospheric seeing, point spread function (PSF) anisotropy and pixelization, incorporated in such a manner as to reproduce actual observations with the William Herschel Telescope. By applying an artificial shear to the simulated images, we test the shear measurement method proposed by Kaiser, Squires & Broadhurst (KSB). Overall, we find the KSB method to be reliable with the following provisos. First, although the recovered shear is linearly related to the input shear, we find a coefficient of proportionality of about 0.8. In addition, we find a residual anti-correlation between the PSF ellipticity and the corrected ellipticities of faint galaxies. To guide future weak lensing surveys, we study the ways in which seeing size, exposure time and pixelization affect the sensitivity to shear. We find that worsened seeing linearly increases the noise in the shear estimate, while the sensitivity depends only weakly on exposure time. The noise is dramatically increased if the pixel scale is larger than that of the seeing. In addition, we study the impact both of overlapping isophotes between neighbouring galaxies, and of PSF correction residuals: together these are found to produce spurious lensing signals on small scales. We discuss the prospects of using the KSB method for future, more sensitive, surveys. Numerical simulations of this kind are a required component of present and future analyses of weak lensing surveys.

Item Type:Article
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URLURL TypeDescription Paper
Ellis, Richard S.0000-0001-7782-7071
Additional Information:© 2001 RAS. Received: 14 March 2001. Accepted: 14 March 2001. Published: 11 August 2001. We would like to thank Thomas Erben, Peter Schneider, Yannick Mellier, Roberto Maoli and Aurélien Thion for useful discussions. We thank the anonymous referee for his thorough review of our manuscript. We are indebted to Nick Kaiser for providing us with the IMCAT software. We acknowledge the invaluable use of IRAF and SEXTRACTOR during this research. AR was supported by a TMR postdoctoral fellowship from the EEC Lensing Network, and by a Wolfson College Research Fellowship. DC acknowledges the ‘Sonderforschungsbereich 375-95 für Astro–Teilchenphysik’ der Deutschen Forschungsgemeinschaft for financial support. This work was supported by the TMR Network ‘Gravitational Lensing: New Constraints on Cosmology and the Distribution of Dark Matter’ of the EC under contract No. ERBFMRX-CT97-0172.
Funding AgencyGrant Number
Wolfson CollegeUNSPECIFIED
Deutsche Forschungsgemeinschaft (DFG)375-95
European CommissionERBFMRX-CT97-0172
Subject Keywords:gravitational lensing, methods: data analysis, techniques: image processing, cosmology: observations, large-scale structure of Universe
Issue or Number:3
Record Number:CaltechAUTHORS:20200527-135432770
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Official Citation:David J. Bacon, Alexandre Refregier, Douglas Clowe, Richard S. Ellis, Numerical simulations of weak lensing measurements, Monthly Notices of the Royal Astronomical Society, Volume 325, Issue 3, August 2001, Pages 1065–1074,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:103499
Deposited By: Rebecca Minjarez
Deposited On:02 Jun 2020 20:04
Last Modified:16 Nov 2021 18:22

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