X射线选择群的入射区和标度关系
Infall Regions and Scaling Relations of X-ray Selected Groups
摘要：
我们使用斯隆数字巡天的第五次数据发布来研究X射线选择的星系群，并将它们的性质与星系团进行比较。我们搜索周围的群体的下落模式，并使用这些来测量大半径的群体质量配置文件。在以前的工作中，我们分析了从ROSAT全天巡天的X射线选择样本的72个集群的下落模式。在这里，我们将这种方法扩展到一个样本的系统较小的X射线通量选择从400平方度的偶然调查的集群和集团ROSAT指出的意见。我们确定了16组SDSS DR 5光谱，寻找下落模式，并计算质量分布2-6 Mpc的群中心与焦散技术。对于这些低质量的星系群，目前还没有其他的质量估算方法可以在如此大的半径下得到，因为维里估算需要动力学平衡，而引力透镜信号太弱。尽管这些群体的规模很小，但大多数都显示出可识别的坠落模式。我们使用焦散和维里质量估计来测量不同观测量之间的标度关系，将这些关系扩展到比许多以前的调查更小的通量和光度。仔细观察发现，其中三个组是较大集群外围的子集群。第四个集团显然正在进行集团与集团的合并。这四个合并组代表标度关系中最极端的离群值。排除这些群体，我们发现$L_X\proptoσ_p^{3.4\pm1.6}$，与以前的集群和组的确定一致。理解星系团和星系群的标度关系对于测量星系团的宇宙学参数是至关重要的。
英文摘要：
We use the Fifth Data Release of the Sloan Digital Sky Survey to study X-ray-selected galaxy groups and compare their properties to clusters. We search for infall patterns around the groups and use these to measure group mass profiles to large radii. In previous work, we analyzed infall patterns for an X-ray-selected sample of 72 clusters from the ROSAT All-Sky Survey. Here, we extend this approach to a sample of systems with smaller X-ray fluxes selected from the 400 Square Degree serendipitous survey of clusters and groups in ROSAT pointed observations. We identify 16 groups with SDSS DR5 spectroscopy, search for infall patterns, and compute mass profiles out to 2-6 Mpc from the group centers with the caustic technique. No other mass estimation methods are currently available at such large radii for these low-mass groups, because the virial estimate requires dynamical equilibrium and the gravitational lensing signal is too weak. Despite the small masses of these groups, most display recognizable infall patterns. We use caustic and virial mass estimates to measure the scaling relations between different observables, extending these relations to smaller fluxes and luminosities than many previous surveys. Close inspection reveals that three of the groups are subclusters in the outskirts of larger clusters. A fourth group is apparently undergoing a group-group merger. These four merging groups represent the most extreme outliers in the scaling relations. Excluding these groups, we find $L_X\proptoσ_p^{3.4\pm1.6}$, consistent with previous determinations for both clusters and groups. Understanding cluster and group scaling relations is crucial for measuring cosmological parameters from clusters.
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