Special Seminar

Speaker: Jun Zhang (Texas)
Title: Conquering Systematic Errors in Weak Lensing Measurements
Date (JST): Wed, Nov 16, 2011, 16:00 - 17:00
Place: Seminar Room A
Related File: 550.pdf
Abstract: Weak gravitational lensing effect causes systematic shape distortions (cosmic shear) of background galaxies, which can be used to probe the properties of the large scale structure and the density profiles of foreground clusters in a model independent way. The key technical difficulty in this field is about how to accurately measure the small cosmic shear signal (typical of order one percent) in the presence of a variable point spread function(PSF), pixelation, noise, high order corrections. In this talk, I will discuss general properties of cosmic shear estimators mostly in an analytical way. More specifically, I will show that:

1. Conventional forms of unbiased shear estimators have strong limitations.
Instead, an alternative form is suggested;

2. Although existing shear estimators all claim to measure the reduced shears, they are not necessarily accurate to the second order in shear/convergence. A useful theorem is found useful for judging the accuracy of any method at second order level given its properties at the first order;

3. Systematic errors caused by PSF, pixelation, and noise can all be removed in well defined ways in Fourier space at least based on the method of Zhang & Komatsu (2011).