The non-Gaussianity of the cosmic shear likelihood or how odd is the Chandra Deep Field South?
The non-Gaussianity of the cosmic shear likelihood or how odd is the Chandra Deep Field South?
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DOI：
10.1051/0004-6361/200911697
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发表时间：
2009-01
影响因子：
6.5
通讯作者：
J. Hartlap;T. Schrabback;P. Simon;P. Schneider
中科院分区：
文献类型：
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作者：
J. Hartlap;T. Schrabback;P. Simon;P. Schneider
目标。我们研究了高斯宇宙剪切似然近似的有效性。我们估计真实的可能性，从一个大的射线追踪模拟的基准宇宙模型和宇宙学参数估计的非高斯性的影响进行调查。我们研究了最近报道的非常低的σ8值有多奇怪，因为它是从钱德拉深场南方（CDFS）使用宇宙剪切导出的，考虑到可能性的非高斯性，以及CDFS选择方式带来的偏差的可能性。方法.由于问题的高维性，通过模拟来估计可能性的蛮力方法必然会失败。因此，我们使用独立分量分析转换的宇宙剪切相关函数到一个新的基础上，其中的可能性近似分解成一个产品的一维分布。结果我们发现，宇宙剪切的可能性是显着的非高斯。这导致后验分布的最大值的偏移和与高斯情况相比显著更小的可信区域。我们重新分析的CDFS宇宙剪切数据使用非高斯的可能性结合保守的星系选择标准，最大限度地减少校准的不确定性。假设CDFS是一个随机指向，我们发现对于固定的Ωm = 0.25，σ8 = 0.68 + 0.09 −0.16。在类似WMAP5的宇宙学中，等于或低于这个值的概率为0.5%。考虑到CDFS的选择方式所产生的偏差，我们将其建模为依赖于CDFS中的晕的数量，我们得到σ8 = 0.71 + 0.10 −0.15。将CDFS数据与WMAP 5的参数约束结合起来，得到平坦宇宙的Ωm = 0.26 + 0.03 −0.02和σ8 = 0.79 + 0.04 −0.03。
Aims. We study the validity of the approximation of a Gaussian cosmic shear likelihood. We estimate the true likelihood for a fiducial cosmological model from a large set of ray-tracing simulations and investigate the impact of non-Gaussianity on cosmological parameter estimation. We investigate how odd the recently reported very low value of σ8 really is as derived from the Chandra Deep Field South (CDFS) using cosmic shear by taking the non-Gaussianity of the likelihood into account, as well as the possibility of biases coming from the way the CDFS was selected. Methods. A brute force approach to estimating the likelihood from simulations must fail because of the high dimensionality of the problem. We therefore use independent component analysis to transform the cosmic shear correlation functions to a new basis, in which the likelihood approximately factorises into a product of one-dimensional distributions. Results. We find that the cosmic shear likelihood is significantly non-Gaussian. This leads to both a shift of the maximum of the posterior distribution and a significantly smaller credible region compared to the Gaussian case. We re-analyse the CDFS cosmic shear data using the non-Gaussian likelihood in combination with conservative galaxy selection criteria that minimise calibration uncertainties. Assuming that the CDFS is a random pointing, we find σ8 = 0.68 +0.09 −0.16 for fixed Ωm = 0.25. In a WMAP5-like cosmology, a value equal to or lower than this would be expected in ≈5% of the times. Taking biases into account arising from the way the CDFS was selected, which we model as being dependent on the number of haloes in the CDFS, we obtain σ8 = 0.71 +0.10 −0.15 . Combining the CDFS data with the parameter constraints from WMAP5 yields Ωm = 0.26 +0.03 −0.02 and σ8 = 0.79 +0.04 −0.03 for a flat universe.