Investigations of a Statistically Complete Sample of Galaxy Clusters

对丰富的星系团的研究提供了许多具有宇宙学重要性的信息。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的蜡烛。尽管它们极其重要，但由于大多数星团都是通过光学板的目视检查发现的，因此从未有过可用于客观统计研究的高红移星团目录。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射线发射特性来寻找星团，大大减少了在可见光波段选择它们时固有的偏差，同时提供了一个具有适合统计分析的可量化特征的目录。对天空中可观测区域进行的最灵敏的x射线观测是由德国卫星ROSAT围绕北黄道极（NEP）进行的。在现有的NSF资助下已经进行的工作表明，x射线数据中处于高红移的星团的数量与预期的一样，并且实际上将提供一个与几十年来使用光学技术积累的样本大致相同大小的样本。这项研究将对ROSAT NEP x射线星团样本进行光学后续研究，特别强调星团的初步鉴定，以及后来对x射线和光学性质的演变、大尺度结构和红外等红移图的研究。与以前的研究相比，ROSAT样品的深度和完整性特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. ***