宇宙学上常见的卫星吸积事件对薄星系的破坏
The Destruction of Thin Stellar Disks Via Cosmologically Common Satellite Accretion Events
摘要：
在LCDM宇宙学中，大多数星系大小的系统（M_host ~ 10^12 M_sun）在过去的8 Gyr中至少吸积了一颗总质量为M_sat ~ 10^11 M_sun = 3 M_disk的卫星。分析和数值研究表明，这是最不稳定的合并类型的薄星系盘的生存，因为更大质量的吸积事件是相对罕见的，质量较小的保存薄盘组件。我们使用高分辨率，无耗散的N体模拟研究的响应初始薄，完全形成的牛奶路型恒星盘这些宇宙学上常见的事件，并表明薄盘不生存。无论轨道配置如何，撞击都将盘转变为大约三倍厚的结构，并且是银河系中观察到的主要薄盘组成部分的两倍多的运动学热。我们的结论是，如果银河系薄盘是一个代表性的情况下，那么稳定的气体成分的存在是唯一的资源来解释的优势盘星系在LCDM宇宙，否则，银河系的磁盘必须是不寻常的冷和薄的亮度，也许是一个异常静止的吸积历史的结果。
英文摘要：
Most Galaxy-sized systems (M_host ~ 10^12 M_sun) in the LCDM cosmology are expected to have accreted at least one satellite with a total mass M_sat ~ 10^11 M_sun = 3M_disk in the past 8 Gyr. Analytic and numerical investigations suggest that this is the most precarious type of merger for the survival of thin galactic disks because more massive accretion events are relatively rare and less massive ones preserve thin disk components. We use high-resolution, dissipationless N-body simulations to study the response of an initially-thin, fully-formed Milky-Way type stellar disk to these cosmologically common events and show that the thin disk does not survive. Regardless of orbital configuration, the impacts transform the disks into structures that are roughly three times as thick and more than twice as kinematically hot as the observed dominant thin disk component of the Milky Way. We conclude that if the Galactic thin disk is a representative case, then the presence of a stabilizing gas component is the only recourse for explaining the preponderance of disk galaxies in an LCDM universe; otherwise, the disk of the Milky Way must be uncommonly cold and thin for its luminosity, perhaps as a consequence of an unusually quiescent accretion history.
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