The Systematic Error Test for PSF Correction in Weak Gravitational Lensing Shear Measurement by the Era Method by Idealizing PSF

Okura, Yuki; Futamase, Toshifumi

doi:10.3847/0004-637x/827/2/138

Cited by 4 publications

(1 citation statement)

References 23 publications

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“…Kaiser et al 1995;Bernstein 2010). These methods can be made quite accurate for galaxy images with high S/N , with little model bias (Bernstein 2010;Okura & Futamase 2016). However, unlike model fitting approaches, missing data and light from nearby objects cannot be "masked-out" or ignored.…”

Section: Introductionmentioning

confidence: 99%

Practical Weak-lensing Shear Measurement with Metacalibration

Sheldon

Huff

2017

ApJ

271

323

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Metacalibration is a recently introduced method to accurately measure weak gravitational lensing shear using only the available imaging data, without need for prior information about galaxy properties or calibration from simulations. The method involves distorting the image with a small known shear, and calculating the response of a shear estimator to that applied shear. The method was shown to be accurate in moderate sized simulations with galaxy images that had relatively high signal-to-noise ratios, and without significant selection effects. In this work we introduce a formalism to correct for both shear response and selection biases. We also observe that, for images with relatively low signal-to-noise ratios, the correlated noise that arises during the metacalibration process results in significant bias, for which we develop a simple empirical correction. To test this formalism, we created large image simulations based on both parametric models and real galaxy images, including tests with realistic point-spread functions. We varied the point-spread function ellipticity at the five percent level. In each simulation we applied a small, few percent shear to the galaxy images. We introduced additional challenges that arise in real data, such as detection thresholds, stellar contamination, and missing data. We applied cuts on the measured galaxy properties to induce significant selection effects. Using our formalism, we recovered the input shear with an accuracy better than a part in a thousand in all cases.

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Section: Introductionmentioning

confidence: 99%

Practical Weak-lensing Shear Measurement with Metacalibration

Sheldon

Huff

2017

ApJ

271

323

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Shear nulling after PSF Gaussianisation: Moment-based weak lensing measurements with subpercent noise bias

Herbonnet

Buddendiek

Kuijken

2017

A&A

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Context. Current optical imaging surveys for cosmology cover large areas of sky. Exploiting the statistical power of these surveys for weak lensing measurements requires shape measurement methods with subpercent systematic errors. Aims. We introduce a new weak lensing shear measurement algorithm, shear nulling after PSF Gaussianisation (SNAPG), designed to avoid the noise biases that affect most other methods. Methods. SNAPG operates on images that have been convolved with a kernel that renders the point spread function (PSF) a circular Gaussian, and uses weighted second moments of the sources. The response of such second moments to a shear of the pre-seeing galaxy image can be predicted analytically, allowing us to construct a shear nulling scheme that finds the shear parameters for which the observed galaxies are consistent with an unsheared, isotropically oriented population of sources. The inverse of this nulling shear is then an estimate of the gravitational lensing shear. Results. We identify the uncertainty of the estimated centre of each galaxy as the source of noise bias, and incorporate an approximate estimate of the centroid covariance into the scheme. We test the method on extensive suites of simulated galaxies of increasing complexity, and find that it is capable of shear measurements with multiplicative bias below 0.5 percent.

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New highly precise weak gravitational lensing flexions measurement method based on ERA method

Okura

Futamase²

2022

Monthly Notices of the Royal Astronomical Society

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Weak gravitational lensing flexions are a kind of weak lensing distortion which are defined as the spin 1 and spin 3 combinations of the third order derivatives of gravitational lensing potential. Since the shear has spin 2 combination of the second order derivative, the flexion signal gives partly independent information from shear signal and is more sensitive to the local mass distribution than shear signal. Thus its measurement is expected to play important roles in observational cosmology. However, since the weakness of the flexion signal as well as the complicatedness of its intrinsic noise made its accurate observation very difficult. We propose a new method of measuring the flexion signal using ERA method which is a method to measure weak lensing shear without any approximation. We find two particular combinations of the flexions which provide the quantities with only lensing information and free of intrinsic noise when taken average. It is confirmed by simple numerical simulation that the statistical average of these combinations do not in fact depend on the strength of the intrinsic distortion. Then, we introduce a method which measures flexions with PSF correction. This method is developed by applying the ERA method for flexion distortions and we call this method the FIRE method. It uses the expansion technique with an assumption of weak flexion, and we show by using typical examples of 1st and 2nd flexion images that the estimated errors become less than 1% in most cases with the lowest order of the expansion. Finally, we apply the method for real data to measure flexion components in real galaxy images.

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The Systematic Error Test for PSF Correction in Weak Gravitational Lensing Shear Measurement by the Era Method by Idealizing PSF

Cited by 4 publications

References 23 publications

Practical Weak-lensing Shear Measurement with Metacalibration

Practical Weak-lensing Shear Measurement with Metacalibration

Shear nulling after PSF Gaussianisation: Moment-based weak lensing measurements with subpercent noise bias

New highly precise weak gravitational lensing flexions measurement method based on ERA method

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