The Clustering of Orbital Poles Induced by the LMC: Hints for the Origin of Planes of Satellites
The Clustering of Orbital Poles Induced by the LMC: Hints for the Origin of Planes of Satellites
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DOI：
10.3847/1538-4357/ac2c05
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发表时间：
2021-08
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通讯作者：
N. Garavito-Camargo;E. Patel;G. Besla;A. Price-Whelan;F. Gómez;C. Laporte;K. Johnston
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作者：
N. Garavito-Camargo;E. Patel;G. Besla;A. Price-Whelan;F. Gómez;C. Laporte;K. Johnston
相当一部分的银河系（MW）卫星表现出与相干轨道平面相一致的相空间特性。利用最近捕获了一颗巨大的（1.8 × 1011 M⊙）lmc类卫星的球形MW光晕的量身定制的n体模拟，我们确定了可能增强绕MW轨道运行的物体轨道极点聚集的物理机制。LMC使MW暗物质粒子的轨道极偏离了目前的随机分布。相反，R≈50kpc以上的粒子的轨道极团位于LMC现在的轨道极附近，沿著天空的正弦模式。在50 ~ 150 kpc （150 ~ 300 kpc）之间，轨道极密度相对于低密度区域δρmax = 30% (50%), δρ iso = 15%（30%）。聚类出现在LMC的中心后（约50 Myr前，49 kpc），持续时间至少1 Gyr。发生聚类的原因有三：(1)LMC改变了MW光晕和盘中心密度的速度和位置；(2) LMC诱导的暗物质动力摩擦尾迹和集体响应改变了粒子的运动学；(3)在空间平面内选择的粒子观测存在偏差，因此在天空中以大圆测量轨道极点会增加其轨道极点聚集的概率。这种情况应该在最近捕获大质量卫星（质量比至少≈1:10）的宿主中普遍存在，导致晕示踪剂的轨道极点聚集。
A significant fraction of Milky Way (MW) satellites exhibit phase-space properties consistent with a coherent orbital plane. Using tailored N-body simulations of a spherical MW halo that recently captured a massive (1.8 × 1011 M ⊙) LMC-like satellite, we identify the physical mechanisms that may enhance the clustering of orbital poles of objects orbiting the MW. The LMC deviates the orbital poles of MW dark matter particles from the present-day random distribution. Instead, the orbital poles of particles beyond R ≈ 50 kpc cluster near the present-day orbital pole of the LMC along a sinusoidal pattern across the sky. The density of orbital poles is enhanced near the LMC by a factor δρmax = 30% (50%) with respect to underdense regions and δ ρ iso = 15% (30%) relative to the isolated MW simulation (no LMC) between 50 and 150 kpc (150–300 kpc). The clustering appears after the LMC’s pericenter (≈50 Myr ago, 49 kpc) and lasts for at least 1 Gyr. Clustering occurs because of three effects: (1) the LMC shifts the velocity and position of the central density of the MW’s halo and disk; (2) the dark matter dynamical friction wake and collective response induced by the LMC change the kinematics of particles; (3) observations of particles selected within spatial planes suffer from a bias, such that measuring orbital poles in a great circle in the sky enhances the probability of their orbital poles being clustered. This scenario should be ubiquitous in hosts that recently captured a massive satellite (at least ≈1:10 mass ratio), causing the clustering of orbital poles of halo tracers.