Cosmic Shears Should Not Be Measured In Conventional Ways

Details Cosmic Shears Should Not Be Measured In Conventional Ways Cosmic Shears Should Not Be Measured In Conventional Ways

2010-02-18

arxiv.org/abs/1002.3615v3

Astronomy and Astrophysics

Astrophysics

Cosmology and Extragalactic Astrophysics

13 pages, MNRAS in press. The title has been changed from "Ideal Cosmic Shear Estimators Do Not Exist" to the current one. Ins

Scientific paper

A long standing problem in weak lensing is about how to construct cosmic shear estimators from galaxy images. Conventional methods average over a single quantity per galaxy to estimate each shear component. We show that any such shear estimators must reduce to a highly nonlinear form when the galaxy image is described by three parameters (pure ellipse), even in the absence of the point spread function (PSF). In the presence of the PSF, we argue that this class of shear estimators do not likely exist. Alternatively, we propose a new way of measuring the cosmic shear: instead of averaging over a single value from each galaxy, we average over two numbers, and then take the ratio to estimate the shear component. In particular, the two numbers correspond to the numerator and denominators which generate the quadrupole moments of the galaxy image in Fourier space, as proposed in Zhang (2008). This yields a statistically unbiased estimate of the shear component. Consequently, measurements of the n-point spatial correlations of the shear fields should also be modified: one needs to take the ratio of two correlation functions to get the desired, unbiased shear correlation.

Affiliated with

Also associated with

No associations

Rating

Cosmic Shears Should Not Be Measured In Conventional Ways does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Cosmic Shears Should Not Be Measured In Conventional Ways, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cosmic Shears Should Not Be Measured In Conventional Ways will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-362580