Biases in, and corrections to, KSB shear measurements

• Verfasst von: Viola, Massimo [VerfasserIn]
• Verfasst von: Melchior, Peter [VerfasserIn]
• Verfasst von: Bartelmann, Matthias [VerfasserIn]
• Titel: Biases in, and corrections to, KSB shear measurements
• Verf.angabe: M. Viola, P. Melchior, M. Bartelmann
• E-Jahr: 2010
• Jahr: 12 Jun 2010
• Umfang: 12 S.
• Fussnoten: Gesehen am 22.09.2017
• Titel Quelle: Enthalten in: De.arxiv.org
• Ort Quelle: [S.l.] : Arxiv.org, 1991
• Jahr Quelle: 2010
• Band/Heft Quelle: (2011) Artikel-Nummer 1006.2470, 12 Seiten
• Datenträger: Online-Ressource
• Sprache: eng
• Sach-SW: Astrophysics - Cosmology and Nongalactic Astrophysics
• Sach-SW: Astrophysics - Astrophysics of Galaxies
• K10plus-PPN: 1563739739

Abstract

We analyse the KSB method to estimate gravitational shear from surface-brightness moments of small and noisy galaxy images. We identify three potentially problematic assumptions. These are: (1) While gravitational shear must be estimated from averaged galaxy images, KSB derives a shear estimate from each individual image and then takes the average. Since the two operations do not commute, KSB gives biased results. (2) KSB implicitly assumes that galaxy ellipticities are small, while weak gravitational lensing assures only that the change in ellipticity due to the shear is small. (3) KSB does not invert the convolution with the point-spread function, but gives an approximate PSF correction which - even for a circular PSF - holds only in the limit of circular sources. The effects of assumptions (2) and (3) partially counter-act in a way dependent on the width of the weight function and of the PSF. We quantitatively demonstrate the biases due to all assumptions, extend the KSB approach consistently to third order in the shear and ellipticity and show that this extension lowers the biases substantially. The issue of proper PSF deconvolution will be addressed in a forthcoming paper.