Investigations of a Statistically Complete Sample of Galaxy Clusters

对丰富星系团的研究提供了许多宇宙学上的重要信息。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，它们最亮的成员星系就一直被用作标准蜡烛。尽管它们极其重要，但从来没有一个高红移星系团的目录可以用于客观的统计研究，因为大多数星系团是通过对光学平板的肉眼检查发现的。星系团也是非常明亮的X射线发射体，因此在对天空的X射线调查中可以发现它们。此外，根据它们的X射线发射特性找到它们大大减少了在可见光波段中选择它们所固有的偏差，同时提供了适合统计分析的具有可量化特征的目录。对天空中可察觉的区域进行的最灵敏的X射线测量是由德国卫星ROSAT围绕北黄道极(NEP)进行的。在现有NSF拨款下已经进行的工作表明，X射线数据中处于高红移的星系团的数量与预期的一样，实际上将提供与几十年来使用光学技术积累的样本大小大致相同的样本。这项研究将对ROSAT NEP X射线星团样本进行光学后续研究，特别是对星团的初步鉴定，以及随后对X射线和光学性质、大尺度结构和红外星等-红移图的演化的研究。与以前的研究相比，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. ***