标题： 最遥远的X射线星系团及其空间密度演化 显示英文标题

标题： The Most Distant X-ray Clusters and the Evolution of their Space Density

摘要： 我们简要回顾了通过几个ROSAT意外巡天测量的遥远X射线团块的空间密度现状。 我们将旧的和新的聚集体X射线光度函数（XLF）的测定结果进行比较，讨论其高红移时具有争议性的演化问题。 我们使用从ROSAT深团块巡天（RDCS）中抽取的完整子样本，量化到z ~1范围内XLF的演化统计显著性。 由此得出了一致的观测结果：大部分团块群体在z ~1范围内没有显著演化，而最亮的系统（L_x >~ L* [0.5-2 keV] =~ 5x10^44 erg/s）确实更稀少，至少在z >0.5时如此，这与EMSS最初的发现相符。 我们还报告了在RDCS中位于z =1以外的四个团块的最新光谱识别结果，这些团块是迄今为止已知最遥远的X射线团块，它们对z >1的团块空间密度设定了有趣的下限。 显示英文摘要

摘要： We briefly review our current knowledge of the space density of distant X-ray clusters as measured by several ROSAT serendipitous surveys. We compare old and new determinations of the cluster X-ray Luminosity Function (XLF) at increasing redshifts, addressing the controversial issue of the evolution of its high end. We use complete subsamples, drawn from the ROSAT Deep Cluster Survey (RDCS), to quantify the statistical significance of the XLF evolution out to z ~1. A consistent observational picture emerges in which the bulk of the cluster population shows no significant evolution out to z ~1, whereas the most luminous systems (L_x >~ L* [0.5-2 keV] =~ 5x10^44 erg/s) were indeed rarer, at least at z >0.5, in keeping with the original findings of the EMSS. We also report on the recent spectroscopic identification of four clusters in the RDCS lying beyond z =1, the most distant X-ray clusters known to date, which set an interesting lower limit on the space density of clusters at z >1.