Calibration biases in measurements of weak lensing
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 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.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- November 2012
- DOI:
- 10.1051/0004-6361/201116983
- arXiv:
- arXiv:1103.5923
- Bibcode:
- 2012A&A...547A..98B
- Keywords:
-
- large-scale structure of Universe;
- cosmological parameters;
- cosmology: observations;
- dark matter;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 5 pages, 3 figures, submitted to A&