发表机构
University of Michigan（密歇根大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过N体模拟和TNG50星系晕数据，发现大质量并合可诱发暗物质晕的四极矩翻滚，该运动保留了晕最后一次主并合的动力学记忆，为ΛCDM理论提供新检验手段。
AI 中文摘要
暗物质晕表现出被称为“图形自转”的缓慢翻滚运动。约80%的孤立ΛCDM晕存在图形自转，且该运动受重子反馈影响较小，使其成为ΛCDM理论的一个有吸引力且相对未被探索的检验手段。然而，星系并合能够对宿主晕的四极矩施加强扭矩，因此有必要研究这类相互作用是否会影响图形自转。本研究利用孤立N体模拟和6个包含银河系（MW）类似星系的TNG50晕，在大质量并合背景下探究图形自转。对于孤立星系，研究发现大质量并合会在两个阶段诱发宿主晕的自转：第一阶段是伴星系落入期间的快速瞬态阶段，自转速度在10°-60°每Gyr之间；第二阶段是并合后的稳态翻滚阶段，自转速度在2°-40°每Gyr之间，且持续至少6-8 Gyr。瞬态和长期翻滚均依赖于落入伴星系的轨迹。研究发现，无轨道角动量的径向并合也能诱发图形自转，表明伴星系的潮汐扭矩是驱动机制。同时，TNG50晕在主并合期间表现出四极矩翻滚的变化：3个晕的自转速度发生改变，6个晕的自转轴方向发生改变。在6个晕中，有5个晕的四极矩翻滚在最后一次主并合后保持稳定。研究结果表明，当前的图形自转可能并非反映早期潮汐切变，而是保留了晕最后一次主并合的动力学记忆。
英文摘要
Dark Matter halos exhibit slow tumbling known as `figure rotation'. Figure rotation occurs in roughly $80\%$ of isolated $Λ$CDM halos and is relatively unaffected by baryonic feedback, making it an attractive and relatively unexplored test for $Λ$CDM. However, galaxy mergers are capable of exerting strong torques on a host halo's quadrupole, warranting an investigation of whether such interactions are capable of influencing figure rotation. Using isolated $N-$body simulations and 6 TNG50 halos containing MW analog galaxies, we investigate figure rotation in the context of massive mergers. For isolated galaxies we find that massive mergers elicit rotation of the host halo in both a rapid transient phase during the satellite infall with pattern speeds between $10^\circ-60^\circ$ Gyr$^{-1}$, and post-merger as a steady tumbling with pattern speeds between $2^\circ-40^\circ$ Gyr$^{-1}$ lasting for at least $6-8$ Gyr. Both transient and long-lived tumbling depend on the trajectory of the infalling satellite. We find that figure rotation can be induced by radial mergers with no orbital angular momentum, suggesting that tidal torques from the satellite are a driving mechanism. Meanwhile, TNG50 halos show quadrupole tumbling modified during major mergers in both pattern speed (3/6 halos) and rotation axis orientation (6/6 halos). Quadrupole tumbling remains stable after the last major merger in 5 of our 6 halos. Our results suggest that, rather than tracing the early tidal shear, figure rotation at present day may instead retain a dynamical memory of a halo's last major merger.
Comments23 pages and 14 figures, accepted to ApJ
