晕内禀对齐的环境依赖性：低密度区域中更强的信号
The Environmental Dependence of Halo Intrinsic Alignments: Stronger Signals in Underdense Regions
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中文总结 AI 辅助
研究暗物质晕内禀对齐与大尺度环境的关系，通过N体模拟，发现低密度环境中晕的IA振幅更大，由晕形状及与潮汐场对齐差异导致，表明大尺度环境对晕和星系对齐模拟很重要。
中文摘要 AI 辅助
星系及其宿主暗物质晕的内禀对齐（IA）是弱引力透镜宇宙学中主要的天体物理系统误差之一，但IA信号如何依赖于晕所在的大尺度环境尚未完全明确。我们利用Dark Quest套件的高分辨率N体模拟来测量红移范围z = 0.1 - 1.5内暗物质晕IA的环境依赖性。通过由8 h⁻¹Mpc内相邻晕的数量定义的过密度δ₈来量化每个晕的环境，并通过比较构建为具有相同晕质量分布的最过密和最欠密晕来将环境效应与其与晕质量依赖性的简并性分离。我们发现，低密度环境中的晕比相同质量的高密度环境中的晕表现出系统上更大的IA振幅A_IA，约为1.5 - 1.8倍，并且这一趋势在探测的质量和红移范围内持续存在，向低红移方向增强。使用仅方向（单位椭圆率）估计器，我们进一步表明这种环境对比度是由两种效应的组合驱动的：低密度区域中的晕本质上比相同质量的高密度对应物更不球形，并且与大尺度潮汐场的对齐更强。这些结果表明，大尺度环境在模拟晕和星系对齐中是一个不可忽略的变量，并且对于超越两点的弱引力透镜分析可能是一个特别重要的因素。
英文摘要
The intrinsic alignment (IA) of galaxies and the dark matter haloes that host them is one of the leading astrophysical systematics for weak-lensing cosmology, yet how the IA signal depends on the large-scale environment in which haloes reside is not yet fully characterised. We use the high-resolution $N$-body simulations of the Dark Quest suite to measure the environmental dependence of the IA of dark matter haloes over the redshift range $z=0.1$--$1.5$. We quantify each halo's environment through the overdensity $δ_8$, defined from the number of neighbouring haloes within $8\, h^{-1}Mpc$, and we isolate the environmental effect from its degeneracy with the halo-mass dependence by comparing the most overdense and most underdense haloes constructed to share the same halo-mass distribution. We find that haloes in underdense environments exhibit systematically larger IA amplitudes $A_{\rm IA}$ than haloes of the same mass in overdense environments, by a factor of $\sim1.5$--$1.8$, and that this trend persists across the mass and redshift ranges probed, strengthening towards low redshift. Using an orientation-only (unit-ellipticity) estimator, we further show that this environmental contrast is driven by a combination of two effects: haloes in underdense regions are both intrinsically less spherical and more strongly aligned with the large-scale tidal field than their overdense counterparts of the same mass. These results indicate that the large-scale environment is a non-negligible variable in modelling halo and galaxy alignments, and may be a particularly important factor for beyond-two-point weak-lensing analyses.
