Bayesian galaxy shape measurement for weak lensing surveys - II. Application to simulations
Bayesian galaxy shape measurement for weak lensing surveys - II. Application to simulations
复制标题
用于弱透镜巡天的贝叶斯星系形状测量 - II。
DOI：
10.1111/j.1365-2966.2008.13628.x
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发表时间：
2008
影响因子：
4.8
通讯作者：
Kitching T
中科院分区：
文献类型：
--
作者：
Kitching T
本文推广了米勒等人提出的贝叶斯模型拟合形状测量方法，并使用该方法从剪切测试程序模拟（STEP）中估计剪切。该方法使用一种快速模型拟合算法，该算法使用真实的星系轮廓，并通过在傅立叶空间中进行模型拟合来分析边缘化模型的位置和幅度。这是用来找到完整的后验概率椭圆。然后从该后验概率表面以贝叶斯方式估计剪切。贝叶斯估计允许去除随机噪声的存在所引起的测量偏差。在本文中，我们介绍了一种迭代算法，它可以用来估计固有椭圆率先验，并证明了这是准确和稳定的。我们使用STEP参数化，通过引入偏置和偏移c将输入剪切γ T与估计的剪切γ M联系起来：γM−γT=mγT+c。STEP1分析中使用的星系平均数密度为每平方弧分9个，STEP2分析中的星系平均数密度为每平方弧分30个。通过使用该方法从STEP1模拟中估计剪切，我们发现该方法具有m = 0.006 ± 0.005的剪切偏差和σc= 0.0002的点扩展函数类型的剪切偏移变化。使用该方法从STEP2模拟中估计剪切，我们发现剪切偏差和偏移分别为m = 0.002 ± 0.016和c =-0.0007 ± 0.0006。此外，我们发现，偏差和偏移是稳定的星系的大小和大小的变化。这种偏差应该产生任何宇宙学的限制，从未来的弱透镜调查鲁棒的系统影响，在形状测量。我们提出了一种STEP参数化的替代方法，即使用一个品质因子，将模拟中的固有剪切方差与测量的剪切方差联系起来，并表明所提出的方法的平均值为Q = 100，至少是10倍于其他形状测量方法。
In this paper, we extend the Bayesian model fitting shape measurement method presented in Miller et al., and use the method to estimate the shear from the Shear TEsting Programme simulations (STEP). The method uses a fast model fitting algorithm that uses realistic galaxy profiles and analytically marginalizes over the position and amplitude of the model by doing the model fitting in Fourier space. This is used to find the full posterior probability in ellipticity. The shear is then estimated in a Bayesian way from this posterior probability surface. The Bayesian estimation allows measurement bias arising from the presence of random noise to be removed. In this paper, we introduce an iterative algorithm that can be used to estimate the intrinsic ellipticity prior and show that this is accurate and stable.We present results using the STEP parametrization that relates the input shear γTto the estimated shear γMby introducing a biasmand an offsetc: γM−γT=mγT+c. The average number density of galaxies used in the STEP1 analysis was 9 per square arcminute, for STEP2 the number density was 30 per square arcminute. By using the method to estimate the shear from the STEP1 simulations we find the method to have a shear bias ofm= 0.006 ± 0.005 and a variation in shear offset with point spread function type of σc= 0.0002. Using the method to estimate the shear from the STEP2 simulations we find that the shear bias and offset arem= 0.002 ± 0.016 andc=−0.0007 ± 0.0006, respectively. In addition, we find that the bias and offset are stable to changes in the magnitude and size of the galaxies. Such biases should yield any cosmological constraints from future weak lensing surveys robust to systematic effects in shape measurement.Finally, we present an alternative to the STEP parametrization by using a quality factor that relates the intrinsic shear variance in a simulation to the variance in shear that is measured and show that the method presented has an average ofQ≳ 100 which is at least a factor of 10 times better than other shape measurement methods.