Early Formation and Late Merging of the Giant Galaxies
Early Formation and Late Merging of the Giant Galaxies
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DOI：
10.1086/423444
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发表时间：
2003-12
期刊：
影响因子：
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通讯作者：
Liang Gao;A. Loeb;P. J. E. Peebles;S. White;A. Jenkins
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文献类型：
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作者：
Liang Gao;A. Loeb;P. J. E. Peebles;S. White;A. Jenkins
目前宇宙中最明亮的星系位于最巨大的暗物质晕的中心：丰富的星系团。在ΛCDM宇宙学中，这种巨大的晕核出现在红移z = 6处，其密度（作为质量内部的函数，约为10 kpc）与今天的值相当。然而，这些中心区域物质的特性预计会发生变化，因为主要的合并将恒星和暗物质从最初分离良好的亚基聚集在一起。我们使用n体模拟来研究这些合并如何将主导星系中预先存在的物质向外推，同时保留无碰撞物质的内部密度分布。看来，大型星系的中心区域最终由大量密集核心形成的恒星主导，这些恒星形成于最后一次大合并之前。这些中心区域的无碰撞物质（恒星和暗物质结合）的密度分布似乎是稳定的，并且在合并时具有类似吸引子的行为。这表明与耗散收缩和恒星形成相关的重子负荷可能会被抹去，因为随后的合并将质量分布推回到一个普遍的剖面。这种对重子载荷影响的抑制，以及质量浓度的早期组装，可能有助于解决CDM模型在结构形成方面的一些明显挑战。
The most luminous galaxies in the present universe are found at the centers of the most massive dark matter halos: rich galaxy clusters. In the ΛCDM cosmology, such massive halo cores are present at redshift z = 6 with a comoving number density (as a function of mass interior to ~10 kpc) that is comparable to today's value. The identity of the matter in these central regions is, however, predicted to change as major mergers bring together stars and dark matter from initially well-separated subunits. We use N-body simulations to investigate how these mergers push preexisting matter outward in the dominant galaxy while preserving the inner density profile of collisionless matter. It appears that the central regions of large galaxies end up dominated by stars formed in a number of dense cores, well before the last major mergers. The density profile of collisionless matter (stars and dark matter combined) in these central regions appears to be stable and to have attractor-like behavior under merging. This suggests that the baryon loading associated with dissipative contraction and star formation may be erased as subsequent mergers drive the mass distribution back to a universal profile. Such suppression of the effects of baryon loading, along with the early assembly of mass concentrations, may help resolve some apparent challenges to the CDM model for structure formation.