大Einstein半径：LambdaCDM的一个问题
Large Einstein Radii: A Problem for LambdaCDM
摘要：
星系团的爱因斯坦半径提供了一个相对独立于模型的质量密度测量，其投影半径为150 kpc，足够大，相对不受气体物理的影响。我们发现，所观察到的爱因斯坦半径的四个良好的研究大规模集群，可靠的维里质量测量，谎言远远超出爱因斯坦半径的预测分布在标准的LambdaCDM模型。基于数值模拟的星系团大小的物体（维里质量约为1 e15太阳）的大样本，预测的爱因斯坦半径只有15- 25“，比这四个星系团观测到的爱因斯坦半径低两倍。这是因为预测的质量分布太浅，不能超过在相当大的投影半径处的透镜化的临界表面密度。在仔细考虑测量误差以及集群选择和透镜测量质量投影中固有的偏差后，我们发现理论预测在4 σ显著性上被排除在外。由于LambdaCDM模型的大多数自由参数现在都建立在坚实的经验基础上，这种差异可能指向一种额外的机制，这种机制可以促进团簇在更早的时间崩溃，从而提高它们的中心质量密度。
英文摘要：
The Einstein radius of a cluster provides a relatively model-independent measure of the mass density of a cluster within a projected radius of ~ 150 kpc, large enough to be relatively unaffected by gas physics. We show that the observed Einstein radii of four well-studied massive clusters, for which reliable virial masses are measured, lie well beyond the predicted distribution of Einstein radii in the standard LambdaCDM model. Based on large samples of numerically simulated cluster-sized objects with virial masses ~ 1e15 solar, the predicted Einstein radii are only 15-25'', a factor of two below the observed Einstein radii of these four clusters. This is because the predicted mass profile is too shallow to exceed the critical surface density for lensing at a sizable projected radius. After carefully accounting for measurement errors as well as the biases inherent in the selection of clusters and the projection of mass measured by lensing, we find that the theoretical predictions are excluded at a 4-sigma significance. Since most of the free parameters of the LambdaCDM model now rest on firm empirical ground, this discrepancy may point to an additional mechanism that promotes the collapse of clusters at an earlier time thereby enhancing their central mass density.
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