银河系暗物质暗晕的形状、方向和排列
The shapes, orientation, and alignment of Galactic dark matter subhalos
摘要：
我们提出了一个研究的形状，方向和银河系暗物质subhalos在"Via Lactea“模拟银河系大小的LCDM主机晕的路线。孤立的暗物质晕倾向于扁长，而暗物质晕主要是三轴的。总的来说，次晕比主晕更接近球形，次轴与主轴的比值为0.68，中间轴与主轴的比值为0.83。与孤立的晕一样，暗晕在其中心区域的球形度往往较低。当形状在物理尺度如r_Vmax（圆速度曲线峰值半径）内测量时，主轴比与晕下质量无关。在靠近主晕中心的地方，暗晕倾向于稍微更接近球形。当它们被最大的V_max选中时，即在它们经历强烈的潮汐质量损失之前，它们的空间分布跟踪着主晕的扁长形状。次晕的方向不是随机的：长轴倾向于与主晕中心的方向对齐。这种对齐对于超过3 r_200的晕消失，并且当在subhalos的外部区域测量形状时更加明显。在次晕的轨道上保持径向排列，并且在近心通过时被拉长，这表明这种排列可能是由主晕的潮汐力引起的。这些潮汐与主晕的相互作用使次晕随着时间的推移变得更圆。
英文摘要：
We present a study of the shapes, orientations, and alignments of Galactic dark matter subhalos in the ``Via Lactea'' simulation of a Milky Way-size LCDM host halo. Whereas isolated dark matter halos tend to be prolate, subhalos are predominantly triaxial. Overall subhalos are more spherical than the host halo, with minor to major and intermediate to major axis ratios of 0.68 and 0.83, respectively. Like isolated halos, subhalos tend to be less spherical in their central regions. The principal axis ratios are independent of subhalo mass, when the shapes are measured within a physical scale like r_Vmax, the radius of the peak of the circular velocity curve. Subhalos tend to be slightly more spherical closer to the host halo center. The spatial distribution of the subhalos traces the prolate shape of the host halo when they are selected by the largest V_max they ever had, i.e. before they experienced strong tidal mass loss. The subhalos' orientation is not random: the major axis tends to align with the direction towards the host halo center. This alignment disappears for halos beyond 3 r_200 and is more pronounced when the shapes are measured in the outer regions of the subhalos. The radial alignment is preserved during a subhalo's orbit and they become elongated during pericenter passage, indicating that the alignment is likely caused by the host halo's tidal forces. These tidal interactions with the host halo act to make subhalos rounder over time.
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