Effects of merging histories on angular momentum distribution of dark matter haloes
Effects of merging histories on angular momentum distribution of dark matter haloes
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合并历史对暗物质晕角动量分布的影响
DOI：
10.1046/j.1365-8711.1998.02053.x
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发表时间：
1997
影响因子：
4.8
通讯作者：
M. Gouda
中科院分区：
文献类型：
--
作者：
M. Gouda
本文分析了原始天体合并历史对现今暗物质晕角动量分布的影响。分析角动量分布的一种解析方法假定，光晕最初是均匀的椭球体，并且光晕角动量的增长在它们的最大膨胀时间停止。然而，最大扩展时间不能被唯一地确定，因为在层级聚类场景中，光晕的每个前辈或子单元都有其自己的最大扩展时间。因此，在估计其角动量时，晕的合并历史可能是很重要的。利用Rodrigues&Thomas的合并树模型，考虑了密度涨落的空间相关性，研究了合并历史对暗物质晕角动量分布的影响。结果发现，合并效应，即最终合并成晕的前体最大膨胀时间的不均匀效应对最终的角动量分布没有强烈的影响，因此齐次椭球近似恰好适合于暗物质晕的角动量分布的估计。这是因为母体角动量方向不同的影响抵消了母体最大膨胀时间不均匀的影响。还研究了两个或多个预先存在的晕合并在一起时轨道角动量对总角动量的贡献。结果表明，扩散吸积物质的角动量对总角动量的贡献比扩散吸积物质的角动量贡献更重要，特别是在多次合并的情况下。
ABSTRA C T The effects of merging histories of proto-objects on the angular momentum distributions of the present-time dark matter haloes are analysed. An analytical approach to the analysis of the angular momentum distributions assumes that the haloes are initially homogeneous ellipsoids and that the growth of the angular momentum of the haloes halts at their maximum expansion time. However, the maximum expansion time cannot be determined uniquely, because in the hierarchical clustering scenario each progenitor, or subunit, of the halo has its own maximum expansion time. Therefore the merging history of the halo may be important in estimating its angular momentum. Using the merger tree model by Rodrigues & Thomas, which takes into account the spatial correlations of the density fluctuations, we have investigated the effects of the merging histories on the angular momentum distributions of dark matter haloes. It was found that the merger effects, that is, the effects of the inhomogeneity of the maximum expansion times of the progenitors which finally merge together into a halo, do not strongly affect the final angular momentum distributions, so that the homogeneous ellipsoid approximation happens to be good for the estimation of the angular momentum distribution of dark matter haloes. This is because the effect of the different directions of the angular momenta of the progenitors cancels out the effect of the inhomogeneity of the maximum expansion times of the progenitors. The contribution of the orbital angular momentum to the total angular momentum when two or more pre-existing haloes merge together was also investigated. It is shown that this contribution is more important than that of the angular momentum of diffuse accreting matter to the total angular momentum, especially when the mergers occur many times.