千年模拟中的银河系化石群的大规模集结
The Mass Assembly of Fossil Groups of Galaxies in the Millennium Simulation
摘要：
千年模拟研究了现今化石星系群的演化。利用千禧年气体模拟和半解析星系表，根据常规观测标准选取红移为零的化石星系群，并对这些星系群对应的晕进行时间回溯，提取出相关的暗物质、气体和星系性质。从这项研究中的化石的空间密度是非常接近观察到的估计和各种可能性的其余差异进行了讨论。X射线明亮系统中化石的比例似乎与观测结果相当一致，模拟预测即使在相当丰富的星系团中，化石系统也会有相当多的发现（占总数的3-4%）。我们发现，与非化石组相比，化石在高红移时组装的质量占其质量的比例更高，在任何时代，化石的当前组装晕质量与最终质量的比率约高出10%至20%。这支持了化石代表未受干扰的早期形成系统的范式，其中大型星系合并形成一个单一的主导椭圆。
英文摘要：
The evolution of present-day fossil galaxy groups is studied in the Millennium Simulation. Using the corresponding Millennium gas simulation and semi-analytic galaxy catalogues, we select fossil groups at redshift zero according to the conventional observational criteria, and trace the haloes corresponding to these groups backwards in time, extracting the associated dark matter, gas and galaxy properties. The space density of the fossils from this study is remarkably close to the observed estimates and various possibilities for the remaining discrepancy are discussed. The fraction of X-ray bright systems which are fossils appears to be in reasonable agreement with observation, and the simulations predict that fossil systems will be found in significant numbers (3-4% of the population) even in quite rich clusters. We find that fossils assemble a higher fraction of their mass at high redshift, compared to non-fossil groups, with the ratio of the currently assembled halo mass to final mass, at any epoch, being about 10 to 20% higher for fossils. This supports the paradigm whereby fossils represent undisturbed, early-forming systems in which large galaxies have merged to form a single dominant elliptical.
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