We study the alignments of satellite galaxies, and their anisotropic distribution, with respect to location and orientation of their host central galaxy in MassiveBlack-II and IllustrisTNG simulations. We find that: the shape of the satellite system in halos of mass ($> 10^{13}h^{-1}M_{\odot}$) is well aligned with the shape of the central galaxy at $z=0.06$ with the mean alignment between the major axes being $\sim \Delta \theta = 12^{\circ}$ when compared to a uniform random distribution; that satellite galaxies tend to be anisotropically distributed along the major axis of the central galaxy with a stronger alignment in halos of higher mass or luminosity; and that the satellite distribution is more anisotropic for central galaxies with lower star formation rate, which are spheroidal, and for red central galaxies.Radially we find that satellites tend to be distributed along the major axis of the shape of the stellar component of central galaxies at smaller scales and the dark matter component on larger scales. We find that the dependence of satellite anisotropy on central galaxy properties and the radial distance is similar in both the simulations with a larger amplitude in MassiveBlack-II. The orientation of satellite galaxies tends to point toward the location of the central galaxy at small scales and this correlation decreases with increasing distance, and the amplitude of satellite alignment is higher in high mass halos. However, the projected ellipticities do not exhibit a scale-dependent radial alignment, as has been seen in some observational measurements.

中文翻译：

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Illustris-TNG 和 MassiveBlack-II 模拟中的群尺度内在星系排列

我们在 MassiveBlack-II 和 IllustrisTNG 模拟中研究卫星星系的排列及其各向异性分布，以及它们的宿主中央星系的位置和方向。我们发现：卫星系统在质量晕圈（$> 10^{13}h^{-1}M_{\odot}$）中的形状与 $z=0.06 处的中央星系的形状很好地对齐$ 与均匀随机分布相比，主轴之间的平均对齐为 $\sim \Delta \theta = 12^{\circ}$；卫星星系倾向于沿中央星系的主轴各向异性分布，在质量或光度更高的光晕中排列更牢固；并且对于恒星形成率较低的球状中央星系和红色中央星系，卫星分布更具各向异性。从径向上，我们发现卫星倾向于沿着较小尺度的中央星系恒星成分和较大尺度的暗物质成分形状的主轴分布。我们发现卫星各向异性对中央星系属性和径向距离的依赖性在 MassiveBlack-II 中具有较大振幅的两个模拟中是相似的。卫星星系的方向在小尺度上倾向于指向中央星系的位置，并且这种相关性随着距离的增加而减小，并且在高质量晕中卫星排列的幅度更高。然而，正如在一些观测测量中所看到的那样，投影椭圆度不表现出与尺度相关的径向排列。