Measurement and calibration of noise bias in weak lensing galaxy shape estimation

Kacprzak, T.; Zuntz, Joe; Rowe, Barnaby; Bridle, Sarah; Réfrégier, Alexandre; Amara, Adam; Voigt, Lisa; Hirsch, Michael

doi:10.1111/j.1365-2966.2012.21622.x

Cited by 97 publications

(131 citation statements)

References 44 publications

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“…Therefore, to estimate errors on the shear calibration, one often relies on image simulations (e.g. Schrabback et al 2007;Kacprzak et al 2012). Image simulations, however, can be problematic if they are not perfectly matched to the datasets in question.…”

Section: Shear Bias Parameterizationmentioning

confidence: 99%

Joint measurement of lensing–galaxy correlations using SPT and DES SV data

Baxter

Clampitt

Giannantonio

et al. 2016

Mon. Not. R. Astron. Soc.

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We measure the correlation of galaxy lensing and cosmic microwave background lensing with a set of galaxies expected to trace the matter density field. The measurements are performed using pre-survey Dark Energy Survey (DES) Science Verification optical imaging data and millimeter-wave data from the 2500 square degree South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) survey. The two lensing-galaxy correlations are jointly fit to extract constraints on cosmological parameters, constraints on the redshift distribution of the lens galaxies, and constraints on the absolute shear calibration of DES galaxy lensing measurements. We show that an attractive feature of these fits is that they are fairly insensitive to the clustering bias of the galaxies used as matter tracers. The measurement presented in this work confirms that DES and SPT data are consistent with each other and with the currently favored ΛCDM cosmological model. It also demonstrates that joint lensing-galaxy correlation measurement considered here contains a wealth of information that can be extracted using current and future surveys.

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Section: Shear Bias Parameterizationmentioning

confidence: 99%

Joint measurement of lensing–galaxy correlations using SPT and DES SV data

Baxter

Clampitt

Giannantonio

et al. 2016

Mon. Not. R. Astron. Soc.

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“…In the presence of noise, however, these estimations suffer from unavoidable biases in the estimated shear (Melchior & Viola 2012;Kacprzak et al 2012). Furthermore, the variance of an estimator such as the mean, or more generally, the scale of the estimator distribution, does depend on the intrinsic ellipticity distribution P(e).…”

Section: Weak Lensingmentioning

confidence: 99%

“…Community-driven projects for optimal and robust shape estimates (Heymans et al 2006;Massey et al 2007;Bridle et al 2010;Kitching et al 2012;Mandelbaum et al 2015) have led to a further decrease in measurement variances and a better understanding of remaining systematic effects and biases (e.g., Voigt & Bridle 2010;Bernstein 2010;Kacprzak et al 2012;Melchior & Viola 2012;Refregier et al 2012).…”

Section: Introductionmentioning

confidence: 99%

Chasing the peak: optimal statistics for weak shear analyses

Smit

Kuijken

2018

A&A

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Context. Weak gravitational lensing analyses are fundamentally limited by the intrinsic distribution of galaxy shapes. It is well known that this distribution of galaxy ellipticity is non-Gaussian, and the traditional estimation methods, explicitly or implicitly assuming Gaussianity, are not necessarily optimal. Aims. We aim to explore alternative statistics for samples of ellipticity measurements. An optimal estimator needs to be asymptotically unbiased, efficient, and robust in retaining these properties for various possible sample distributions. We take the non-linear mapping of gravitational shear and the effect of noise into account. We then discuss how the distribution of individual galaxy shapes in the observed field of view can be modeled by fitting Fourier modes to the shear pattern directly. This allows scientific analyses using statistical information of the whole field of view, instead of locally sparse and poorly constrained estimates. Methods. We simulated samples of galaxy ellipticities, using both theoretical distributions and data for ellipticities and noise. We determined the possible bias ∆e, the efficiency η and the robustness of the least absolute deviations, the biweight, and the convex hull peeling estimators, compared to the canonical weighted mean. Using these statistics for regression, we have shown the applicability of direct Fourier mode fitting. Results. We find an improved performance of all estimators, when iteratively reducing the residuals after de-shearing the ellipticity samples by the estimated shear, which removes the asymmetry in the ellipticity distributions. We show that these estimators are then unbiased in the absence of noise, and decrease noise bias by more than ∼ 30%. Our results show that the convex hull peeling estimator distribution is skewed, but still centered around the underlying shear, and its bias least affected by noise. We find the least absolute deviations estimator to be the most efficient estimator in almost all cases, except in the Gaussian case, where it's still competitive (0.83 < η < 5.1) and therefore robust. These results hold when fitting Fourier modes, where amplitudes of variation in ellipticity are determined to the order of 10 −3 . Conclusions. The peak of the ellipticity distribution is a direct tracer of the underlying shear and unaffected by noise, and we have shown that estimators that are sensitive to a central cusp perform more efficiently, potentially reducing uncertainties by more than 50% and significantly decreasing noise bias. These results become increasingly important, as survey sizes increase and systematic issues in shape measurements decrease.

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“…The better-fitting model is then used to give an ellipticity estimate. Maximum-likelihood parameter sets computed by im3shape and similar codes have a bias we refer to as noise bias [32,33]. This bias is removed using a calibration scheme based on the work of Kacprzak et al [33].…”

Section: A Shear Measurement Pipeline 1: Ngmixmentioning

confidence: 99%

“…Maximum-likelihood parameter sets computed by im3shape and similar codes have a bias we refer to as noise bias [32,33]. This bias is removed using a calibration scheme based on the work of Kacprzak et al [33]. The scheme is applied to an ensemble of galaxies using the mean bias calibration for the ensemble; different subsets of objects thus use different correction factors.…”

Section: A Shear Measurement Pipeline 1: Ngmixmentioning

confidence: 99%

Cosmic shear measurements with Dark Energy Survey Science Verification data

Becker¹,

Troxel²,

MacCrann³

et al. 2016

Phys. Rev. D

Self Cite

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We present measurements of weak gravitational lensing cosmic shear two-point statistics using Dark Energy Survey Science Verification data. We demonstrate that our results are robust to the choice of shear measurement pipeline, either ngmix or im3shape, and robust to the choice of twopoint statistic, including both real and Fourier-space statistics. Our results pass a suite of null tests including tests for B-mode contamination and direct tests for any dependence of the twopoint functions on a set of 16 observing conditions and galaxy properties, such as seeing, airmass, galaxy color, galaxy magnitude, etc. We furthermore use a large suite of simulations to compute the covariance matrix of the cosmic shear measurements and assign statistical significance to our null tests. We find that our covariance matrix is consistent with the halo model prediction, indicating that it has the appropriate level of halo sample variance. We compare the same jackknife procedure applied to the data and the simulations in order to search for additional sources of noise not captured by the simulations. We find no statistically significant extra sources of noise in the data. The overall detection significance with tomography for our highest source density catalog is 9.7σ. Cosmological constraints from the measurements in this work are presented in a companion paper [1].

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Measurement and calibration of noise bias in weak lensing galaxy shape estimation

Cited by 97 publications

References 44 publications

Joint measurement of lensing–galaxy correlations using SPT and DES SV data

Joint measurement of lensing–galaxy correlations using SPT and DES SV data

Chasing the peak: optimal statistics for weak shear analyses

Cosmic shear measurements with Dark Energy Survey Science Verification data

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