寻找化石群：光学鉴定和X射线确证
Finding Fossil Groups: Optical Identification and X-ray Confirmation
摘要：
我们报告发现了12个新的化石星系群，这些星系群主要由一个巨大的椭圆星系和星系团规模的引力势组成，但缺乏通常在星系团中看到的明亮星系群。这些化石群（FG），从maxBCG光学星团目录中选择，在钱德拉X射线天文台的快照观测中检测到。我们详细介绍了非常成功的选择方法，从我们的目标样本15个候选人中识别12个FG的成功率为80%。对于11个系统，我们确定的X射线光度，温度和流体静力学质量，这并不偏离正常系统的预期显着，跨越一个典型的丰富的集团和穷人的星系团的范围。少数检测到的FG形态不规则，可能是由于过去的合并，集团内介质（IGM）与中央AGN的相互作用，或多个大质量晕的叠加。三分之二的X射线检测到的FG表现出与中央BCG相关的X射线发射，尽管我们无法使用当前数据区分活动星系核和扩展热星系发射。这个样本是已知FG数量的大幅增加，对于未来计划的观测将是非常宝贵的，以确定FG温度，气体密度，金属丰度和质量分布，并与正常（非化石）系统进行比较。最后，缺乏星系的系统的人口的存在可能会使质量函数的确定产生偏差，这些质量函数从星系数量来测量丰富度。当用于约束功率谱归一化和Ω_m时，这些有偏的质量函数可能反过来使这些结果有偏。
英文摘要：
We report the discovery of 12 new fossil groups of galaxies, systems dominated by a single giant elliptical galaxy and cluster-scale gravitational potential, but lacking the population of bright galaxies typically seen in galaxy clusters. These fossil groups (FGs), selected from the maxBCG optical cluster catalog, were detected in snapshot observations with the Chandra X-ray Observatory. We detail the highly successful selection method, with an 80% success rate in identifying 12 FGs from our target sample of 15 candidates. For 11 of the systems, we determine the X-ray luminosity, temperature, and hydrostatic mass, which do not deviate significantly from expectations for normal systems, spanning a range typical of rich groups and poor clusters of galaxies. A small number of detected FGs are morphologically irregular, possibly due to past mergers, interaction of the intra-group medium (IGM) with a central AGN, or superposition of multiple massive halos. Two-thirds of the X-ray-detected FGs exhibit X-ray emission associated with the central BCG, although we are unable to distinguish between AGN and extended thermal galaxy emission using the current data. This sample, a large increase in the number of known FGs, will be invaluable for future planned observations to determine FG temperature, gas density, metal abundance, and mass distributions, and to compare to normal (non-fossil) systems. Finally, the presence of a population of galaxy-poor systems may bias mass function determinations that measure richness from galaxy counts. When used to constrain power spectrum normalization and Ω_m, these biased mass functions may in turn bias these results.
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