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Abstract: Gravitational lensing shear has the potential to be the most powerful toolfor constraining the nature of dark energy. However, accurate measurement ofgalaxy shear is crucial and has been shown to be non-trivial by the ShearTEsting Programme. Here we demonstrate a fundamental limit to the accuracyachievable by model-fitting techniques, if oversimplistic models are used. Weshow that even if galaxies have elliptical isophotes, model-fitting methodswhich assume elliptical isophotes can have significant biases if they use thewrong profile. We use noise-free simulations to show that on allowingsufficient flexibility in the profile the biases can be made negligible. Thisis no longer the case if elliptical isophote models are used to fit galaxiesmade up of a bulge plus a disk, if these two components have differentellipticities. The limiting accuracy is dependent on the galaxy shape but wefind the most significant biases for simple spiral-like galaxies. Theimplications for a given cosmic shear survey will depend on the actualdistribution of galaxy morphologies in the universe, taking into account thesurvey selection function and the point spread function. However our resultssuggest that the impact on cosmic shear results from current and near futuresurveys may be negligible. Meanwhile, these results should encourage thedevelopment of existing approaches which are less sensitive to morphology, aswell as methods which use priors on galaxy shapes learnt from deep surveys.



Autor: L.M. Voigt, S. L. Bridle

Fuente: https://arxiv.org/







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