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arXiv 1108.2202astro-ph.CO
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三轴星系团的弱透镜效应

Weak lensing by triaxial galaxy clusters

F. Feroz, M. P. Hobson

摘要:

星系团的弱引力透镜研究通常假设一个球形的星系团模型来简化分析,但最近的一些研究表明,这种简化的假设可能会导致估计的星系团质量和浓度值有很大的偏差,因为星系团预计会表现出三轴性。然而,几个这样的分析引用了三轴模型中透镜势的空间导数的表达式,这容易引起误解。本文给出了三轴NFW星系团的弱透镜效应的清晰描述,并提出了一种有效而稳健的方法来模拟这些星系团并获得参数估计。通过考虑四个高度三轴NFW星系团,我们重新审视简化球形假设的影响,发现虽然浓度估计基本上是无偏的,除了在我们的一个traixial NFW模拟集群,其中的浓度只有轻微的偏见,质量显着偏置,高达40%,我们分析的所有集群。此外,我们发现,这样的假设可能会导致错误的结论,即一些子结构存在于星系团,甚至更糟的是,多个星系团存在于该领域。我们的聚类拟合方法还允许回答一个问题,即给定的聚类是否具有三轴性或简单的球形模型是不够好。

英文摘要:

Weak gravitational lensing studies of galaxy clusters often assume a spherical cluster model to simplify the analysis, but some recent studies have suggested this simplifying assumption may result in large biases in estimated cluster masses and concentration values, since clusters are expected to exhibit triaxiality. Several such analyses have, however, quoted expressions for the spatial derivatives of the lensing potential in triaxial models, which are open to misinterpretation. In this paper, we give a clear description of weak lensing by triaxial NFW galaxy clusters and also present an efficient and robust method to model these clusters and obtain parameter estimates. By considering four highly triaxial NFW galaxy clusters, we re-examine the impact of simplifying spherical assumptions and found that while the concentration estimates are largely unbiased except in one of our traixial NFW simulated clusters, for which the concentration is only slightly biased, the masses are significantly biased, by up to 40%, for all the clusters we analysed. Moreover, we find that such assumptions can lead to the erroneous conclusion that some substructure is present in the galaxy clusters or, even worse, that multiple galaxy clusters are present in the field. Our cluster fitting method also allows one to answer the question of whether a given cluster exhibits triaxiality or a simple spherical model is good enough.

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