2012A&A...547A..98B -
Astronomy and Astrophysics, volume 547A, 98-98 (2012/11-1)
Calibration biases in measurements of weak lensing.
BARTELMANN M., VIOLA M., MELCHIOR P. and SCHAEFER B.M.
Abstract (from CDS):
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 Ωm0 and σ8. 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.
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Journal keyword(s):
large-scale structure of Universe - cosmological parameters - cosmology: observations - dark matter
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