大质量星系团从z~0到z~1.9的显著相似性
The Remarkable Similarity of Massive Galaxy Clusters From z~0 to z~1.9
摘要：
我们给出了在南极望远镜2500 deg^2巡天中对8个z>1.2的最大质量星系团进行钱德拉X射线巡天的结果。我们将这个样本与先前发表的Chandra观测结果相结合，其中包括49个0<z<0.1的大质量X射线选择集群和90个0.25<z<1.2的SZ选择集群，以限制集群内介质（ICM）在过去~10 Gyr的演化。我们发现，在这里探测的整个红移范围内，ICM的大部分都是自相似地演化的，在r>0.2R500处的ICM密度与E（z）^2相似。在团簇的中心（r<0.1R500），我们发现了与自相似性的显著偏离（n_e ~ E（z）^{0.1+/-0.5}），与没有红移依赖性相一致。当我们隔离具有过密核心的集群时（即，冷核），我们发现平均过密度轮廓并没有随着红移而演变-也就是说，冷核在过去的9-10 Gyr中没有改变大小，密度或总质量。我们表明，不断发展的“尖”的集群在X射线，报告了以前的几项研究，可以理解的背景下，一个冷的核心与固定的属性嵌入在一个自我相似的不断发展的集群。我们没有发现可测量的大质量星系团的X射线形态的演变，似乎与宇宙学模拟预测的快速上升（红移）的主要合并率的紧张局势。我们表明，如果我们假设合并后的弛豫时间与交叉时间成正比，这两个结果可以达成一致，因为后者与H（z）^（-1）成正比。
英文摘要：
We present the results of a Chandra X-ray survey of the 8 most massive galaxy clusters at z>1.2 in the South Pole Telescope 2500 deg^2 survey. We combine this sample with previously-published Chandra observations of 49 massive X-ray-selected clusters at 0<z<0.1 and 90 SZ-selected clusters at 0.25<z<1.2 to constrain the evolution of the intracluster medium (ICM) over the past ~10 Gyr. We find that the bulk of the ICM has evolved self similarly over the full redshift range probed here, with the ICM density at r>0.2R500 scaling like E(z)^2. In the centers of clusters (r<0.1R500), we find significant deviations from self similarity (n_e ~ E(z)^{0.1+/-0.5}), consistent with no redshift dependence. When we isolate clusters with over-dense cores (i.e., cool cores), we find that the average over-density profile has not evolved with redshift -- that is, cool cores have not changed in size, density, or total mass over the past ~9-10 Gyr. We show that the evolving "cuspiness" of clusters in the X-ray, reported by several previous studies, can be understood in the context of a cool core with fixed properties embedded in a self similarly-evolving cluster. We find no measurable evolution in the X-ray morphology of massive clusters, seemingly in tension with the rapidly-rising (with redshift) rate of major mergers predicted by cosmological simulations. We show that these two results can be brought into agreement if we assume that the relaxation time after a merger is proportional to the crossing time, since the latter is proportional to H(z)^(-1).
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