标题： 质量分布和亚晕吸积 显示英文标题

标题： Mass distribution and accretion of sub-halos

摘要： 我们利用“千年模拟”研究了暗晕组装历史中合并事件期间吸积亚晕的质量函数。 我们的研究包括三种亚晕合并类型：（1）发生在暗晕主要前身上的合并；（2）发生在整个暗晕合并树上的合并；以及（3）在现今暗晕中留下可识别亚晕的合并。 我们估算了未演化的亚晕质量函数（USMF），其中亚晕质量是在它们被吸积时测量的。 对于合并到现今暗晕主分支中的亚晕，其USMF可以用一种通用的形式很好地描述，并与先前的结果高度一致。 对于在整个晕合并历史中合并成为亚晕的所有前身的USMF，也可以得出相同的结论。 在这两种情况下，USMF也独立于宿主晕的红移。 由于潮汐瓦解，只有很少一部分吸积的晕能作为可识别的亚晕在现今的暗晕中幸存下来。 在星团大小的晕中，约有30%的幸存亚晕是次级亚晕，并且这个比例随着晕质量的减小而下降。 对于给定的晕和亚晕质量，吸积时间具有非常宽广的分布，但所有幸存的亚晕都是相当近期被吸积的。 显示英文摘要

摘要： We use the "Millennium Simulation" to study the mass function of accreted sub-halos during merger events in the dark halo assembly history. Our study includes three kinds of sub-halo mergers: (1) mergers that happen to the main progenitor of dark halos; (2) mergers that happen on the entire merging history tree of dark halos; and (3) mergers that leave identifiable sub-halos in present-day dark halos. We estimate the unevolved sub-halo mass functions (USMFs), for which sub-halo masses are measured at the times of their accretion. For sub-halos that merge into the main branch of a present-day dark halo, their USMF can be well described by a universal functional form, in excellent agreement with previous results. The same conclusion can also be reached for the USMF of all progenitors that have merged to become sub-halos during the entire halo merging history. In both cases, the USMFs are also independent of the redshift of host halos. Due to tidal disruption, only a small fraction of the accreted halos survive as sub-halos identifiable in the present-day dark halos. In cluster-sized halos, about 30% of the survived sub-halos are sub-subhalos, and this fraction decreases with decreasing halo mass. For given halo and sub-halo masses, the accretion time has very broad distribution, but the survived sub-halos are all accreted quite recently.