[论文解读] A stream come true: Connecting tidal tails, shells, streams, and planes with galaxy kinematics and formation history

Lucas M. Valenzuela, Rhea–Silvia Remus|arXiv (Cornell University)|Aug 17, 2022

Galaxies: Formation, Evolution, Phenomena参考文献 1被引用 4

一句话总结

本研究利用Magneticum Pathfinder流体动力学宇宙学模拟，将潮汐特征（壳层、流、尾迹和卫星平面）与星系运动学及形成历史相联系。研究发现，壳层与慢速旋转星系中的径向并合有关，而流则强烈指示具有运动学分离核心的星系中发生多次小质量并合，揭示轨道角动量是星系演化中的关键因素。

ABSTRACT

The rapidly improving quality and resolution of both low surface brightness observations and cosmological simulations of galaxies enables one to address the important question how the formation history is imprinted in the outer, unrelaxed regions of galaxies, and to inspect the correlations of such imprints with the internal kinematics. Using the hydrodynamical cosmological simulation Magneticum Pathfinder, we identify tidal tails, shells, streams, and satellite planes, and connect their existence to the amount of rotational support and the formation histories of the host galaxies. This presents the first combined statistical census considering all those four types of features in hydrodynamical cosmological simulations. Tidal features are visually classified from a 3D rendering of the simulated galaxies by several scientists. The results are compared to observations, especially from the MATLAS survey. Prominent features are more common around elliptical than around disk galaxies. Shells are preferentially found around kinematically slowly rotating galaxies in both simulations and observations, while streams only have a slight preference to be present around slowly rotating galaxies. Tails and satellite planes appear independently of the internal kinematics of the central galaxy, indicating that they are formed through processes that have not (yet) affected the internal kinematics. As shells are formed through radial merger events while streams are remnants of circular merger infall, this suggests that the orbital angular momentum of the merger event plays a more crucial role in transforming the host galaxy than previously anticipated. The existence of shells around slow rotators is further a sign of a radial merger formation for the particular slow rotators, as a third of the galaxies with a shell were transformed into slow rotators by the merger event that also caused the shells.

研究动机与目标

• 在流体动力学模拟中，统计关联潮汐特征（壳层、流、尾迹、卫星平面）与星系运动学及形成历史。
• 确定旋转支持与内部运动学结构如何影响潮汐特征的存在。
• 检验潮汐特征是否更常出现在特定并合路径（如径向与环形轨道）形成的星系中。
• 将模拟结果与MATLAS巡天的观测数据进行比较，以验证模拟的预测能力。
• 阐明轨道角动量在塑造潮汐特征与星系运动学中的作用。

提出的方法

• 由多位独立科学家通过3D渲染图像对潮汐特征进行目视分类，仅当至少一半分类者识别出某特征时才予以计数。
• 从Magneticum Pathfinder模拟的前期分析中提取运动学属性，包括旋转支持与运动学分离核心（KDCs）的存在情况。
• 通过并合树与吸积卫星的轨道角动量推断形成历史，区分径向（形成壳层）与环形（形成流）轨道。
• 将潮汐特征的出现概率与宿主星系运动学（包括扁球状旋转星系与慢速旋转星系）进行统计相关性分析。
• 将结果与MATLAS巡天的观测数据进行对比，以验证模拟的真实性与预测准确性。
• 分析速度弥散与运动学图，以探测壳层的间接信号，例如低速度弥散区域。

实验结果

研究问题

• RQ1 在宇宙学模拟中，壳层、流、尾迹与卫星平面等潮汐特征如何与宿主星系的旋转支持相关联？
• RQ2 吸积卫星的轨道角动量与特定潮汐特征（如壳层与流）的形成之间存在何种关联？
• RQ3 运动学分离核心（KDCs）在多大程度上表明星系经历了多并合形成路径，如流的存在所暗示的那样？
• RQ4 为何扁球状旋转星系更可能拥有多个潮汐特征？这与其形成历史有何关联？
• RQ5 卫星平面是否与潮汐特征共同演化，还是代表一种先于动力学与形态变化的并合前状态？

主要发现

• 壳层主要出现在运动学上慢速旋转的星系周围，其中30%的壳层宿主星系因形成壳层的并合事件而成为慢速旋转星系。
• 流在具有运动学分离核心（KDCs）的星系中最为普遍，近20%的KDC星系表现出流，表明其经历了多并合形成路径。
• 扁球状旋转星系拥有最高的整体潮汐特征宿主概率，表明其为多次并合事件形成的过并合系统。
• 尾迹与卫星平面与宿主星系运动学无显著相关性，表明其形成过程尚未影响星系内部动力学。
• 壳层在运动学图中表现为低速度弥散区域，但在速度图中不可见，表明速度弥散是探测暗淡外区壳层的更灵敏指标。
• 潮汐特征与卫星平面之间无强相关性，表明后者可能代表并合前状态，或与潮汐特征形成机制不同的独立形成途径。