The XXL Survey XXXIII. Chandra constraints on the AGN contamination of z > 1 XXL galaxy clusters
The XXL Survey XXXIII. Chandra constraints on the AGN contamination of z > 1 XXL galaxy clusters
复制标题
XXL 调查 XXXIII。
DOI：
10.1051/0004-6361/201833654
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发表时间：
2018
影响因子：
6.5
通讯作者：
Logan C
中科院分区：
文献类型：
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作者：
Logan C
XMM-XXL巡天利用XMM-牛顿天文台的观测数据来探测质量和红移范围很广的星系团。中等PSF（轴上半高宽~ 6″）意味着星团内的点源或投射到星团上的点源可能与星团发射不分离，本文介绍了XMM-XXL巡天中观测到的21个红移z> 1的星系团和候选星系团的Chandra短时间观测结果。方法利用Chandra的上级角分辨率，我们调查在簇区域内是否存在未被XMM-XXL分析管道检测到的任何点源，以及是否有任何点源被错误地分类为远距离簇。9是免费的显着点源污染，要么没有以前未解决的来源检测Chandraor与小于约10%的报告XXL集群通量被分解成点源。在其他五个来源中，一个被以前未解决的活动星系核严重污染，四个似乎是活动星系核被错误归类为星系团。除了一种情况之外，所有这些情况都在不太安全的X射线选择簇检测的子集中，并且假阳性率与XXL选择函数建模的预期一致。我们还考虑了另外七个光学选择的集群候选人与暗淡XXL源，不归类为集群。其中三个被Chandra证明是活动星系核，一个是XXL测量通量被未分辨活动星系核高度污染的星系团，而三个似乎是未污染的星系团。通过净化和检查这些遥远的星系团，我们提供了一个纯样本的星系团在redshiftz> 1更深入的后续观测，并证明了实用的使用的AGN快照测试活动星系核的调查与高灵敏度，但角分辨率差。
ContextThe XMM-XXL survey has used observations from theXMM-Newtonobservatory to detect clusters of galaxies over a wide range in mass and redshift. The moderate PSF (FWHM~ 6″ on-axis) ofXMM-Newtonmeans that point sources within or projected onto a cluster may not be separated from the cluster emission, leading to enhanced luminosities and affecting the selection function of the cluster survey.AimsWe present the results of shortChandraobservations of 21 galaxy clusters and cluster candidates at redshiftsz> 1 detected in the XMM-XXL survey in X-rays or selected in the optical and infra-red.MethodsWith the superior angular resolution ofChandra, we investigate whether there are any point sources within the cluster region that were not detected by the XMM-XXL analysis pipeline, and whether any point sources were misclassified as distant clusters.ResultsOf the 14 X-ray selected clusters, 9 are free from significant point source contamination, either having no previously unresolved sources detected byChandraor with less than about 10% of the reported XXL cluster flux being resolved into point sources. Of the other five sources, one is significantly contaminated by previously unresolved AGN, and four appear to be AGN misclassified as clusters. All but one of these cases are in the subset of less secure X-ray selected cluster detections and the false positive rate is consistent with that expected from the XXL selection function modelling. We also considered a further seven optically selected cluster candidates associated with faint XXL sources that were not classed as clusters. Of these, three were shown to be AGN byChandra, one is a cluster whose XXL survey flux was highly contaminated by unresolved AGN, while three appear to be uncontaminated clusters. By decontaminating and vetting these distant clusters, we provide a pure sample of clusters at redshiftz> 1 for deeper follow-up observations, and demonstrate the utility of usingChandrasnapshots to test for AGN in surveys with high sensitivity but poor angular resolution.