期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 425, 期 3, 页码 1951-1957出版社
OXFORD UNIV PRESS
DOI: 10.1111/j.1365-2966.2012.21483.x
关键词
gravitational lensing: weak; methods: statistical; techniques: image processing; cosmology: observations; dark energy; dark matter
资金
- Royal Society
- European Research Council [240672]
- STFC [ST/J001511/1, ST/F001991/1, ST/I000879/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/I000879/1, ST/J001511/1] Funding Source: researchfish
Weak lensing experiments are a powerful probe into cosmology through their measurement of the mass distribution of the universe. A challenge for this technique is to control systematic errors that occur when measuring the shapes of distant galaxies. In this paper, we investigate noise bias, a systematic error that arises from second-order noise terms in the shape measurement process. We first derive analytical expressions for the bias of general maximum-likelihood estimators in the presence of additive noise. We then find analytical expressions for a simplified toy model in which galaxies are modelled and fitted with a Gaussian with its size as a single free parameter. Even for this very simple case we find a significant effect. We also extend our analysis to a more realistic six-parameter elliptical Gaussian model. We find that the noise bias is generically of the order of the inverse-squared signal-to-noise ratio (SNR) of the galaxies and is thus of the order of a percent for galaxies of SNR 10, i.e. comparable to the weak lensing shear signal. This is nearly two orders of magnitude greater than the systematic requirements for future all-sky weak lensing surveys. We discuss possible ways to circumvent this effect, including a calibration method using simulations discussed in an associated paper.
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