Calibration biases in measurements of weak lensing
Abstract
As shown recently, the common KSB method for measuring weak gravitational shear creates a nonlinear relation between the measured and the true ellipticity of objects. We investigate here what effect such a nonlinear calibration relation may have on cosmological parameter estimates from weak lensing if a simpler, linear calibration relation is assumed. We show that the nonlinear relation introduces a bias in the shearcorrelation amplitude and thus a bias in the cosmological parameters Ω_{m0} and σ_{8}. Its direction and magnitude depends on whether the pointspread 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 cosmologicalparameter estimates from measurements of weak lensing, one must verify that the method employed is free from ellipticitydependent 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:
 10.1051/00046361/201116983
 arXiv:
 arXiv:1103.5923
 Bibcode:
 2012A&A...547A..98B
 Keywords:

 largescale structure of Universe;
 cosmological parameters;
 cosmology: observations;
 dark matter;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 5 pages, 3 figures, submitted to A&