The strongest gravitational lenses - II. Is the large Einstein radius of MACS J0717.5+3745 in conflict with ΛCDM?
The strongest gravitational lenses - II. Is the large Einstein radius of MACS J0717.5+3745 in conflict with ΛCDM?
复制标题
最强引力透镜 - II MACS J0717 5 3745 的大爱因斯坦半径与 ÎCDM 冲突吗？
DOI：
10.1051/0004-6361/201219944
复制
发表时间：
2012
影响因子：
6.5
通讯作者：
M. Bartelmann
中科院分区：
文献类型：
--
作者：
J.-C. Waizmann;M. Redlich;M. Bartelmann
背景随着星系团数据数量和质量的不断提高，是否可以基于单个观测到的极端星系团来质疑标准宇宙学模型的问题就出现了。通常，“极端”这个词直接指的是团簇质量，它不是直接可观察到的，因此存在很大的不确定性。因此，有必要将极端星团的研究扩展到直接观测，例如爱因斯坦半径。目的我们的目标是评估标准ΛCDM宇宙学中MACS J0717.5+3745的大观测爱因斯坦半径的出现概率。特别是，我们想要对给定宇宙体积中单个最大爱因斯坦半径的分布函数进行建模，并研究哪些基本假设和效应对结果影响最大。方法我们基于过去光锥上光晕群体的半解析模型，通过蒙特卡罗方法获得了该分布。对分布进行采样后，我们将结果与一般极值（GEV）分布进行拟合，用于后续分析。结果我们发现最大爱因斯坦半径的分布对晕质量函数、透镜三轴性、晕密度轮廓的内斜率和质量浓度关系的精确选择特别敏感。利用如此获得的分布，我们研究了 MACS J0717.5+3745 大爱因斯坦半径的出现概率，发现该系统与 ΛCDM 不存在张力。我们还发现，GEV 分布可以用来非常准确地拟合采样分布，并且所有这些分布都可以用（II 型）Fréchet 分布来描述。 结论 由于多种效应强烈影响单个最大爱因斯坦半径的分布，因此基于单个观测结果可以排除标准 ΛCDM 宇宙学是非常值得怀疑的。尽管基本假设存在很大的不确定性，但如果有人想要这样做，就必须观察到比 MACS J0717.5+3745 大得多的爱因斯坦半径 (≳100″)。
ContextWith the amount and quality of galaxy cluster data increasing, the question arises whether or not the standard cosmological model can be questioned on the basis of a single observed extreme galaxy cluster. Usually, the wordextremerefers directly to cluster mass, which is not a direct observable and thus subject to substantial uncertainty. Hence, it is desirable to extend studies of extreme clusters to direct observables, such as the Einstein radius.AimsWe aim to evaluate the occurrence probability of the large observed Einstein radius of MACS J0717.5+3745 within the standard ΛCDM cosmology. In particular, we want to model the distribution function of the single largest Einstein radius in a given cosmological volume and to study which underlying assumptions and effects have the strongest impact on the results.MethodsWe obtain this distribution by a Monte Carlo approach, based on the semi-analytic modelling of the halo population on the past lightcone. After sampling the distribution, we fit the results with the general extreme value (GEV) distribution which we use for the subsequent analysis.ResultsWe find that the distribution of the maximum Einstein radius is particularly sensitive to the precise choice of the halo mass function, lens triaxiality, the inner slope of the halo density profile and the mass-concentration relation. Using the distributions so obtained, we study the occurrence probability of the large Einstein radius of MACS J0717.5+3745, finding that this system is not in tension with ΛCDM. We also find that the GEV distribution can be used to fit very accurately the sampled distributions and that all of them can be described by a (type-II) Fréchet distribution.ConclusionsWith a multitude of effects that strongly influence the distribution of the single largest Einstein radius, it is more than doubtful that the standard ΛCDM cosmology can be ruled out on the basis of a single observation. If, despite the large uncertainties in the underlying assumptions, one wanted to do so, a much larger Einstein radius (≳100″) than that of MACS J0717.5+3745 would have to be observed.