Inside out and upside-down: The roles of gas cooling and dynamical heating in shaping the stellar age–velocity relation
Inside out and upside-down: The roles of gas cooling and dynamical heating in shaping the stellar age–velocity relation
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DOI：
10.1093/mnras/stab289
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发表时间：
2020-05
影响因子：
4.8
通讯作者：
J. Bird;S. Loebman;D. Weinberg;A. Brooks;T. Quinn;C. Christensen
中科院分区：
文献类型：
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作者：
J. Bird;S. Loebman;D. Weinberg;A. Brooks;T. Quinn;C. Christensen
盘星系的运动学研究，使用银河系中的单个恒星或随时间推移的全球盘运动学的统计研究，提供了对盘如何形成和演化的深入了解。我们使用一个高分辨率的，宇宙学的变焦模拟银河系质量盘星系（h277）捆绑在一起的本地光盘运动学和光盘随时间的演变。现今h277的恒星年龄-速度关系（AVR）与银河系中类似的太阳邻域测量几乎相同。这一成功的一个关键因素是模拟的动态冷多相ISM，它允许年轻恒星以低速分散形成（σ诞生$\sim \！6 - 8 \ \mathrm{km\，s}^{-1}$）晚些时候。较老的恒星在出生时运动学上更热（即圆盘随着时间的推移以“颠倒”的形式形成），并且在出生后随后被加热。圆盘也是“由内向外”生长的，由于径向混合，现在太阳附近的许多较老的恒星都存在。我们证明了h277中σ诞生的演化可以用描述盘星系中从z = 2-3到现在观测到的速度色散普遍减小的相同模型来解释，其中盘在准稳定平衡中演化，ISM速度色散随着时间的推移由于气体分数的减少而减小。因此，我们的研究结果绑在一起的银河系的AVR与观察到的运动学的高z盘星系的本地观测。
Kinematic studies of disc galaxies, using individual stars in the Milky Way or statistical studies of global disc kinematics over time, provide insight into how discs form and evolve. We use a high-resolution, cosmological zoom-simulation of a Milky Way-mass disc galaxy (h277) to tie together local disc kinematics and the evolution of the disc over time. The present-day stellar age–velocity relationship (AVR) of h277 is nearly identical to that of the analogous solar-neighbourhood measurement in the Milky Way. A crucial element of this success is the simulation’s dynamically cold multiphase ISM, which allows young stars to form with a low velocity dispersion (σbirth$\sim \!6 - 8 \ \mathrm{km\, s}^{-1}$) at late times. Older stars are born kinematically hotter (i.e. the disc settles over time in an ‘upside-down’ formation scenario), and are subsequently heated after birth. The disc also grows ‘inside-out’, and many of the older stars in the present-day solar neighbourhood are present because of radial mixing. We demonstrate that the evolution of σbirth in h277 can be explained by the same model used to describe the general decrease in velocity dispersion observed in disc galaxies from z ∼ 2–3 to the present-day, in which the disc evolves in quasi-stable equilibrium and the ISM velocity dispersion decreases over time due to a decreasing gas fraction. Thus, our results tie together local observations of the Milky Way’s AVR with observed kinematics of high z disc galaxies.