95 research outputs found
A new weak lensing shear analysis method using ellipticity defined by 0th order moments
We developed a new method that uses ellipticity defined by 0th order moments
(0th-ellipticity) for weak gravitational lensing shear analysis. Although there
is a strong correlation between the ellipticity calculated using this approach
and the usual ellipticity defined by the 2nd order moment, the ellipticity
calculated here has a higher signal-to-noise ratio because it is weighted to
the central region of the image. These results were confirmed using data for
Abell 1689 from the Subaru telescope. For shear analysis, we adopted the
ellipticity of re-smeared artificial image (ERA) method for point spread
function (PSF) correction, and we tested the precision of this 0th-ellipticity
with simple simulation, then we obtained the same level of precision with the
results of ellipticity defined by quadrupole moments. Thus, we can expect that
weak lensing analysis using 0 shear will be improved in proportion to the
statistical error.Comment: 25pages, 8figures; published by A&A 201
Elliptical Weighted HOLICs for Weak Lensing Shear Measurement. part1:Definitions and isotropic PSF correction
We develop a new method to estimate gravitational shear by adopting an
elliptical weight function to measure background galaxy images. In doing so, we
introduce a new concept of "zero plane" which is an imaginal source plane where
shapes of all sources are perfect circles, and regard the intrinsic shear as
the result of an imaginal lensing distortion. This makes the relation between
the observed shear, the intrinsic shear and lensing distortion more simple and
thus higher-order calculation more easy. The elliptical weight function allows
us to measure the mutiplemoment of shape of background galaxies more precisely
by weighting highly to brighter parts of image and moreover to reduce
systematic error due to insufficient expansion of the weight function in the
original approach of KSB. Point Spread Function(PSF) correction in E-HOLICs
methods becomes more complicated than those in KSB methods. In this paper we
studied isotropic PSF correction in detail. By adopting the lensing distortion
as the ellipticity of the weight function, we are able to show that the shear
estimation in E-HOLICs method reduces to solve a polynomial in the absolute
magnitude of the distortion. We compare the systematic errors between our
approach and KSB using STEP2 simulation. It is confirmed that KSB method
overestimate the input shear for images with large ellipticities, and E-HOLICs
correctly estimate the input shear even for such images. Anisotropic PSF
correction and analysis of real data will be presented in forthcoming paper.Comment: 30 pages, 8 figures, submitted to Ap
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