Investigations of a Statistically Complete Sample of Galaxy Clusters

AST 95-00515 PI：J.帕特里克亨利 对丰富星系团的研究提供了许多宇宙学上重要的信息。它们是最早发现暗物质的地方，从现代研究宇宙的年龄和命运开始，它们最明亮的成员星系就被用作标准烛光。尽管它们极其重要，但从来没有一个可以用于客观统计研究的高红移星系团目录，因为大多数星系团是通过光学板的目视检查发现的。 星系团也是非常明亮的X射线发射器，因此它们在天空的X射线调查中被发现。此外，通过它们的X射线发射特性发现集群大大减少了在可见波段选择它们时固有的偏差，同时提供了一个具有适用于统计分析的可量化特征的目录。德国卫星ROSAT在北极附近进行的X射线观测是对天空中一个可观区域最灵敏的观测。在现有的NSF资助下已经进行的工作表明，X射线数据中高红移的簇的数量与预期的一样，实际上将提供与使用光学技术数十年来积累的样本大小相同的样本。这项调查将光学后续研究的ROSAT NEP X射线集群样本，特别强调的初始识别的集群和后来的调查的演变的X射线和光学性质，大尺度结构，和红外星等红移图。与以往的研究相比，ROSAT样本的深度和完整性将使这些领域得到重大改进。 ***

AST 95-00515 PI: J. Patrick Henry The study of rich clusters of galaxies provides much information of cosmological importance. They were the first places where dark matter was found. Their brightest member galaxies have been used as standard candles from the inception of modern investigations into the age and fate of the Universe. Despite their extreme importance, there has never been a catalog of clusters at high redshifts that could be used for objective statistical studies because most clusters are found from visual inspection of optical plates. Clusters of galaxies are also very luminous X-ray emitters, hence they are found in X-ray surveys of the sky. Further, finding clusters by their X-ray emission properties greatly reduces biases inherent in selecting them in the visible band while simultaneously providing a catalog with quantifiable characteristics suitable for statistical analysis. The most sensitive X-ray survey of an appreciable region of the sky is that performed by the German satellite ROSAT around the North Ecliptic Pole (NEP). Work already performed under an existing NSF grant shows that the number of clusters at high redshifts in the X-ray data is as expected, and will in fact provide a sample of about the same size as that accumulated after decades of effort using optical techniques. This investigation will optically follow-up studies of the ROSAT NEP X-ray cluster sample with particular emphasis on the initial identifications of the clusters and later investigations of evolution of X-ray and optical properties, large scale structure, and the infrared magnitude-redshift diagram. The depth and completeness properties of the ROSAT sample will enable significant improvements to be made in these areas compared to previous studies. ***