Measurement and calibration of noise bias in weak lensing galaxy shape estimation
2012
Weak gravitational lensing has the potential to constrain cosmological parameters to high
precision. However, as shown by the Shear Testing Programmes and Gravitational lensing
Accuracy Testing challenges, measuring galaxy shears is a non-trivial task: various methods
introduce different systematic biases which have to be accounted for. We investigate how
pixel noise on the image affects the bias on shear estimates from a maximum likelihood
forward model-fitting approach using a sum of co-elliptical Sersic profiles, in complement
to the theoretical approach of an associated paper. We evaluate the bias using a simple but
realistic galaxy model and find that the effects of noise alone can cause biases of the order of
1–10 per cent on measured shears, which is significant for current and future lensing surveys.
We evaluate a simulation-based calibration method to create a bias model as a function of
galaxy properties and observing conditions. This model is then used to correct the simulated
measurements. We demonstrate that, for the simple case in which the correct range of galaxy
models is used in the fit, the calibration method can reduce noise bias to the level required for
estimating cosmic shear in upcoming lensing surveys.
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