TITLE:
Shear calibration biases in weak lensing surveys.
AUTHOR(S):
Christopher M. Hirata, Uros Seljak (Princeton University)
DATE:
2003 Jan 04 (arXiv, posted, v1);
2003 Jan 04 (MNRAS, submitted);
2003 Apr 01 (revised);
2003 Apr 04 (MNRAS, accepted);
2003 Apr 04 (arXiv, posted, v2);
2003 Jul 22 (MNRAS, published).
AVAILABILITY: arXiv
astro-ph/0301054 (free); Blackwell-Synergy (requires subscription)
PUBLICATION INFORMATION: Monthly Notices of the Royal Astronomical Society, 343, 459-480
(2003), 22 pages.
ABSTRACT: We investigate biases induced by the conversion between the observed image shape to
shear distortion in current weak lensing analysis methods. Such overall calibration biases cannot be detected by the standard tests such
as E/B decomposition or calibration with stars. We find that the non-Gaussianity of point spread function has a significant effect and
can lead to up to 15 per cent error on the linear amplitude of fluctuations s8 depending on the
method of analysis. This could explain some of the discrepancies seen in recent amplitude determinations from weak lensing. Using an
elliptical Laguerre expansion method we develop a re-Gaussianization method which reduces the error to calibration error of order 1 per
cent even for poorly resolved galaxies. We also discuss a new type of shear selection bias which results in up to roughly 8 percent
underestimation of the signal. It is expected to scale with redshift, inducing errors in the growth factor extraction if not properly
corrected for. Understanding and correcting for such effects is crucial if weak lensing is to become a high precision probe of
cosmology.
ADS BIBLIOGRAPHIC CODE:
2003MNRAS.343..459H
COMMENTS:
At the time of this paper, measurements of the amplitude of density perturbations in the universe using weak
gravitational lensing of galaxies had yielded a variety of values of this amplitude varying by of order 20%. We
proposed that part
of the reason involved shear calibration errors, including incomplete correction for the blurring effect of the
atmosphere on the galaxy images and a selection bias related to galaxy shape; in any event, we suggested that
high-accuracy cosmological measurements using weak lensing would have to take these effects into account more
accurately.