Cosmic shear requirements on the wavelength dependence of telescope point spread functions
Cosmic shear requirements on the wavelength dependence of telescope point spread functions
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DOI：
10.1111/j.1365-2966.2010.16461.x
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发表时间：
2010-01
影响因子：
4.8
通讯作者：
E. Cypriano;A. Amara;L. Voigt;S. Bridle;F. Abdalla;A. Réfrégier;M. Seiffert;J. Rhodes
中科院分区：
文献类型：
--
作者：
E. Cypriano;A. Amara;L. Voigt;S. Bridle;F. Abdalla;A. Réfrégier;M. Seiffert;J. Rhodes
宇宙切变需要在存在模糊图像的观测点扩散函数(PSF)的情况下对星系形状进行高精度测量。因此，每个星系的PSF必须是高精度的。然而，由于几个原因，PSF通常是波长相关的；因此，观测对象的光谱能量分布之间的差异带来了进一步的复杂性。在本文中，我们研究了PSF的波长依赖性的影响，重点是PSF尺寸由望远镜的衍射极限决定的仪器，以及使用宽带滤光片进行形状测量的仪器。我们首先计算了当使用未校正的恒星PSF时，从宇宙切变估计宇宙学参数的偏差。使用真实的星系和恒星光谱能量分布和群体，以及一个简单的三分量圆形PSF，我们发现在下一代望远镜中必须考虑颜色相关性。然后我们考虑了两种不同的方法来消除这种影响：(I)使用与星系相同颜色的恒星和(Ii)使用多种颜色和使用望远镜模型来估计星系光谱能量分布。我们发现，这两种方法都可以将影响修正到低于测量暗能量参数的百分比能级所需的容差的水平。这两种方法的比较有利于模板拟合法，因为它的效率对星系红移的依赖比宽带色法小，并充分利用了更深层次的光度测量。
Cosmic shear requires high precision measurement of galaxy shapes in the presence of the observational point spread function (PSF) that smears out the image. The PSF must therefore be known for each galaxy to a high accuracy. However, for several reasons, the PSF is usually wavelength dependent; therefore, the differences between the spectral energy distribution of the observed objects introduce further complexity. In this paper, we investigate the effect of the wavelength dependence of the PSF, focusing on instruments in which the PSF size is dominated by the diffraction limit of the telescope and which use broad-band filters for shape measurement. We first calculate biases on cosmological parameter estimation from cosmic shear when the stellar PSF is used uncorrected. Using realistic galaxy and star spectral energy distributions and populations and a simple three-component circular PSF, we find that the colour dependence must be taken into account for the next generation of telescopes.We then consider two different methods for removing the effect: (i) the use of stars of the same colour as the galaxies and (ii) estimation of the galaxy spectral energy distribution using multiple colours and using a telescope model for the PSF. We find that both of these methods correct the effect to levels below the tolerances required for per cent level measurements of dark energy parameters. Comparison of the two methods favours the template-fitting method because its efficiency is less dependent on galaxy redshift than the broad-band colour method and takes full advantage of deeper photometry.