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arXiv 2302.01307astro-ph.GA
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非轴对称影响:棒旋星系中依赖半径和角度的趋势

The Non-Axisymmetric Influence: Radius and Angle-Dependent Trends in a Barred Galaxy

Carrie Filion, Rachel L. McClure, Martin D. Weinberg, Elena D'Onghia, Kathryne J. Daniel

AI总结:

本研究利用 N 体模拟分析星系棒导致的径向混合,揭示恒星迁移随方位角和半径变化的三区结构,并探讨用金属度趋势反演初始梯度与重排历史。

摘要:

许多盘星系都拥有星系棒,它会施加随时间变化的非轴对称力,从而改变恒星的轨道。由棒导致的恒星径向重排(“径向混合”)应当同时具有角度依赖性和半径依赖性;我们在此通过分析这些因素的共同影响,给出新的结果和趋势。我们使用一项 N 体模拟,通过在棒形成后不同时刻对一系列环带中的轨道半径变化进行量化,来研究棒形成之后盘中恒星粒子径向位置的变化。我们发现,对于恒星进入给定环带所移动的中位距离,棒诱导出了同时依赖方位角和半径的趋势。在我们考察的所有半径处都存在角度依赖趋势,而半径依赖趋势大致将盘划分为三个“区域”。在内区,恒星通常起源于更大的半径,其轨道向内演化。外区中的恒星很可能起源于更小的半径,其轨道向外演化。在中间区,轨道不存在净的向内或向外演化。我们采用一个具有半径依赖初始金属度梯度的简单玩具模型,并在该模型背景下讨论近期关于银河系中角度依赖恒星金属度变化的观测证据。我们还简要评述了利用观测到的角度依赖金属度趋势来认识盘中曾经存在的初始金属度梯度以及所发生径向重排的可能性。

英文摘要:

Many disc galaxies host galactic bars, which exert time-dependent, non-axisymmetric forces that can alter the orbits of stars. There should be both angle and radius-dependence in the resulting radial rearrangement of stars ('radial mixing') due to a bar; we present here novel results and trends through analysis of the joint impact of these factors. We use an N-body simulation to investigate the changes in the radial locations of star particles in a disc after a bar forms by quantifying the change in orbital radii in a series of annuli at different times post bar-formation. We find that the bar induces both azimuth angle- and radius- dependent trends in the median distance that stars have travelled to enter a given annulus. Angle-dependent trends are present at all radii we consider, and the radius-dependent trends roughly divide the disc into three 'zones'. In the inner zone, stars generally originated at larger radii and their orbits evolved inwards. Stars in the outer zone likely originated at smaller radii and their orbits evolved outwards. In the intermediate zone, there is no net inwards or outwards evolution of orbits. We adopt a simple toy model of a radius-dependent initial metallicity gradient and discuss recent observational evidence for angle-dependent stellar metallicity variations in the Milky Way in the context of this model. We briefly comment on the possibility of using observed angle-dependent metallicity trends to learn about the initial metallicity gradient(s) and the radial rearrangement that occurred in the disc.

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