Calibration biases in measurements of weak lensing

Abstract

As recently shown by Viola et al., the common (KSB) method for measuring weak gravitational shear creates a non-linear relation between the measured and the true shear 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 Omega_matter and sigma_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 measured. 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.

5 pages, 3 figures, submitted to A&A

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• Cosmic shear measurement with maximum likelihood and maximum a posteriori inference
• Magnification bias in the shear-ratio test: a viable mitigation strategy
• De-noising the galaxies in the Hubble XDF with EMPCA
• Refined position angle measurements for galaxies of the SDSS Stripe 82 co-added dataset