Limitations of model-fitting methods for lensing shear estimation
Limitations of model-fitting methods for lensing shear estimation
复制标题
DOI：
10.1111/j.1365-2966.2010.16300.x
复制
发表时间：
2009-05
影响因子：
4.8
通讯作者：
L. Voigt;S. Bridle
中科院分区：
文献类型：
--
作者：
L. Voigt;S. Bridle
引力透镜剪切有可能成为限制暗能量性质的最有力的工具。然而，准确测量星系剪切是至关重要的，并已被证明是不平凡的剪切测试计划。在这里，我们展示了一个基本的限制，通过模型拟合技术实现的准确性，如果过于简单的模型使用。我们表明，即使星系有椭圆等照度线，模型拟合方法，假设椭圆等照度线可以有显着的偏差，如果他们使用错误的配置文件。我们使用无噪声模拟来表明，在轮廓中允许足够的灵活性时，偏差可以忽略不计。如果椭圆等照度线模型被用来拟合由一个凸起和一个圆盘组成的星系，如果这两个组成部分有不同的椭圆度，情况就不再是这样了。有限的精度取决于星系的形状，但我们发现最显着的偏差（类似于1%的剪切）简单的螺旋状星系。对于一个给定的宇宙剪切调查的影响将取决于星系形态在宇宙中的实际分布，考虑到调查选择函数和点扩散函数。然而，我们的研究结果表明，从目前和不久的将来的调查宇宙剪切结果的影响可能是微不足道的。与此同时，这些结果应该鼓励现有的方法，这是不太敏感的形态，以及使用的方法，从深调查了解到的星系形状先验的发展。
Gravitational lensing shear has the potential to be the most powerful tool for constraining the nature of dark energy. However, accurate measurement of galaxy shear is crucial and has been shown to be non-trivial by the Shear TEsting Programme. Here, we demonstrate a fundamental limit to the accuracy achievable by model-fitting techniques, if oversimplistic models are used. We show that even if galaxies have elliptical isophotes, model-fitting methods which assume elliptical isophotes can have significant biases if they use the wrong profile. We use noise-free simulations to show that on allowing sufficient flexibility in the profile the biases can be made negligible. This is no longer the case if elliptical isophote models are used to fit galaxies made up of a bulge plus a disc, if these two components have different ellipticities. The limiting accuracy is dependent on the galaxy shape, but we find the most significant biases (similar to 1 per cent of the shear) for simple spiral-like galaxies. The implications for a given cosmic shear survey will depend on the actual distribution of galaxy morphologies in the Universe, taking into account the survey selection function and the point spread function. However, our results suggest that the impact on cosmic shear results from current and near future surveys may be negligible. Meanwhile, these results should encourage the development of existing approaches which are less sensitive to morphology, as well as methods which use priors on galaxy shapes learnt from deep surveys.