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arXiv 1111.5780astro-ph.CO
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重子冷却对浓度-质量关系的影响

The effects of baryonic cooling on the concentration-mass relation

C. Fedeli

摘要:

我重新审视维里质量和浓度之间的关系,在最近的一些工作中测量的星系群和星系团。正如几位作者以前所指出的,低质量星系团和星系群显示出系统性的更大的浓度,而不是基于纯粹的$n$体模拟的简单处方所预测的。这意味着观察到的浓度-质量关系的斜率/归一化比理论研究预期的大得多。此外,这一结论似乎是相当独立的选择效果,持有透镜和X射线为基础的集群样本。为了阐明这个问题,我采用了一个简单的球形晕模型,除了暗物质,还包含恒星和热扩散气体的比例和分布与最近的观察。此外,我还包括了暗物质由于结构本身非常中心部分的重子冷却而经历的收缩效应。由此产生的修正浓度-质量关系比理论输入的关系更陡峭,因为恒星形成在低质量物体中的效率要高一些。然而,该效应在所有质量下都是非零的,因此也导致更大的归一化。总的来说,新的关系提供了一个更好的表示观察到的几乎所有的目录中考虑这项工作,虽然具体的细节取决于相当显着的重子分数处方通过。无论如何,同样的效应也可以通过重子在结构内的重新分配来产生。最后,我用这个简单的模型来说明宇宙结构的估计浓度是如何被高估的,作为分析所涵盖的径向范围的函数。(节略)

英文摘要:

I re-examine the relation between virial mass and concentration for groups and clusters of galaxies as measured in a number of recent works. As previously noted by several authors, low-mass clusters and groups of galaxies display systematically larger concentrations than simple prescriptions based on pure $n$-body simulations would predict. This implies an observed concentration-mass relation with a substantially larger slope/normalization than expected from theoretical investigations. Additionally, this conclusion seems to be quite independent on selection effects, holding for both lensing based and X-ray based cluster samples. In order to shed new light on this issue I employ a simple spherical halo model containing, in addition to dark matter, also stars and hot diffuse gas in proportions and with distributions in agreement with the most recent observations. Moreover, I include the contraction effect experienced by dark matter due to the cooling of baryons in the very central part of the structure itself. The resulting modified concentration-mass relation is steeper than the theoretical input one, because star formation is fractionally more efficient in low-mass objects. However, the effect is non-vanishing at all masses, thus resulting also in a larger normalization. Overall the new relation provides a better representation of the observed one for almost all catalogs considered in this work, although the specific details depend quite significantly on the baryon fraction prescription adopted. Anyhow, the same effect could also be produced by a redistribution of baryons within the structure. Finally I use this simple model to show how the estimated concentration of cosmic structures is expected to be overestimated as a function of the radial range covered by the analysis. (abridged)

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