We use a high-resolution cosmological dark matter-only simulation to study the orbital trajectories of haloes and subhaloes in the environs of isolated hosts. We carefully tally all apsis points and use them to distinguish haloes that are infalling for the first time from those that occupy more evolved orbits. We find that roughly 21 per cent of subhaloes within a host's virial radius are currently on first infall, and have not yet reached their first orbital pericentre; roughly 44 per cent are still approaching their first apocentre after infall. For the range of host masses studied, roughly half of all accreted systems were pre-processed prior to infall, and about 20 per cent were accreted in groups. We confirm that the entire population of accreted subhaloes -- often referred to as "associated" subhaloes -- extend far beyond the virial radii of their hosts, with roughly half currently residing at distances that exceed $\approx 1.2\times r_{200}$. Many of these backsplash haloes have gained orbital energy since infall, and occupy extreme orbits that carry them well past their initial turnaround radii. Such extreme orbits are created during the initial accretion and dissolution of loosely bound groups, but also through penetrating encounters between subhaloes on subsequent orbits. The same processes may also give rise to unexpectedly abrupt losses of orbital energy. These effects combine, giving rise to a large variation in the ratio of sequent apocentres for accreted systems. We find that, within 2 virial radii from host centres, the concentrations of first-infall halos are remarkably similar those of isolated field halos, whereas backsplash haloes, as well as systems that were pre-processed, are considerably more concentrated.

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相关亚晕的预处理、群吸积和轨道轨迹

我们使用高分辨率宇宙学暗物质模拟来研究孤立宿主环境中晕和亚晕的轨道轨迹。我们仔细计算所有的顶点，并使用它们来区分第一次落入的晕圈和那些占据更进化轨道的晕圈。我们发现，宿主的维里半径内大约 21% 的亚晕目前处于第一次下降，尚未到达它们的第一个轨道中心；大约 44% 的人仍在接近他们在下降后的第一个中心点。对于所研究的宿主质量范围，大约一半的吸积系统在落入之前进行了预处理，大约 20% 是成组吸积的。我们确认整个吸积亚晕群——通常被称为“相关的” 亚晕——远远超出其宿主的维里半径，目前大约有一半的距离超过 $\approx 1.2\times r_{200}$。许多这些后溅光晕自落入以来就获得了轨道能量，并占据了使它们远远超过其初始回转半径的极端轨道。这种极端轨道是在松散结合群的初始吸积和溶解过程中产生的，但也是通过后续轨道上亚晕之间的穿透相遇而产生的。同样的过程也可能导致轨道能量意外地突然损失。这些影响结合在一起，导致了吸积系统的后续中心点比率的巨大变化。我们发现，在距宿主中心 2 维里半径范围内，初入晕的浓度与孤立场晕的浓度非常相似，