### Abstract

As shown recently, the common KSB method for measuring weak gravitational shear creates a non-linear relation between the measured and the true ellipticity of objects. We investigate here what effect such a non-linear calibration relation may have on cosmological parameter estimates from weak lensing if a simpler, linear calibration relation is assumed. We show that the non-linear relation introduces a bias in the shear-correlation amplitude and thus a bias in the cosmological parameters Ω _{m0} and σ _{8}. Its direction and magnitude depends on whether the point-spread function is narrow or wide compared to the galaxy images from which the shear is estimated. Substantial over-or underestimates of the cosmological parameters are equally possible, depending also on the variant of the KSB method. Our results show that for trustable cosmological-parameter estimates from measurements of weak lensing, one must verify that the method employed is free from ellipticity-dependent biases or monitor that the calibration relation inferred from simulations is applicable to the survey at hand.

Original language | English (US) |
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Article number | A98 |

Journal | Astronomy and Astrophysics |

Volume | 547 |

DOIs | |

State | Published - 2012 |

### All Science Journal Classification (ASJC) codes

- Astronomy and Astrophysics
- Space and Planetary Science

### Keywords

- Cosmological parameters
- Cosmology: observations
- Dark matter
- Large-scale structure of Universe

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## Cite this

*Astronomy and Astrophysics*,

*547*, [A98]. https://doi.org/10.1051/0004-6361/201116983