Snails across Scales: Local and Global Phase-mixing Structures as Probes of the Past and Future Milky Way
Snails across Scales: Local and Global Phase-mixing Structures as Probes of the Past and Future Milky Way
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DOI：
10.3847/1538-4357/ac47f7
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发表时间：
2021-07
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影响因子：
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通讯作者：
Suroor S. Gandhi;K. Johnston;Jason A. S. Hunt;A. Price-Whelan;C. Laporte;D. Hogg
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作者：
Suroor S. Gandhi;K. Johnston;Jason A. S. Hunt;A. Price-Whelan;C. Laporte;D. Hogg
在银河系(MW‘s)的盘面上观察到了垂直不平衡的特征。这些特征局部地表现为z-v z空间中的未混合的相螺旋(“蜗牛-同相”)，而全局表现为非零均值z和v-z，在x-y平面上围绕磁盘形成物理螺旋(“蜗牛-空间”)。我们通过卫星扰动测试粒子类MW盘的例子来探索这些局部螺旋和全局螺旋之间的联系。我们预计我们的结果将广泛适用于任何垂直扰动。使用z-v z不对称度规，我们证明了在测试粒子模拟中：(A)当恒星被单一事件(在我们的例子中，是卫星盘交叉)激发的方位作用Jϕ入仓时，出现了多个局部相螺旋形态；(B)这些不同的相螺旋可以追溯到不同的盘位置；以及(C)它们在不同的时间被激发。因此，局部位相螺旋从多个角度提供了微波扰动历史的全局视图。使用人马座(SGR)类卫星穿过磁盘的玩具模型，我们证明了完全相互作用发生在与R≲10kpc内磁盘星的轨道周期相当的时间尺度上。因此，这种扰动具有广泛的影响，在不同时间在盘的不同区域达到峰值。这导致我们检查正在进行的MW-SGR相互作用。虽然SGR还没有越过磁盘(目前，z SGR≈−6 kpc，v z，SGR≈210 KM S−1)，但我们证明撞击的峰值已经过去。SGR对过去150MyR的拉动产生了幅度为∝M SGR的全球v-z信号，这可能在未来的光谱调查中可以检测到。
Signatures of vertical disequilibrium have been observed across the Milky Way’s (MW’s) disk. These signatures manifest locally as unmixed phase spirals in z–v z space (“snails-in-phase”), and globally as nonzero mean z and v z , wrapping around the disk into physical spirals in the x–y plane (“snails-in-space”). We explore the connection between these local and global spirals through the example of a satellite perturbing a test-particle MW-like disk. We anticipate our results to broadly apply to any vertical perturbation. Using a z–v z asymmetry metric, we demonstrate that in test-particle simulations: (a) multiple local phase-spiral morphologies appear when stars are binned by azimuthal action J ϕ , excited by a single event (in our case, a satellite disk crossing); (b) these distinct phase spirals are traced back to distinct disk locations; and (c) they are excited at distinct times. Thus, local phase spirals offer a global view of the MW’s perturbation history from multiple perspectives. Using a toy model for a Sagittarius (Sgr)–like satellite crossing the disk, we show that the full interaction takes place on timescales comparable to orbital periods of disk stars within R ≲ 10 kpc. Hence such perturbations have widespread influence, which peaks in distinct regions of the disk at different times. This leads us to examine the ongoing MW–Sgr interaction. While Sgr has not yet crossed the disk (currently, z Sgr ≈ −6 kpc, v z,Sgr ≈ 210 km s−1), we demonstrate that the peak of the impact has already passed. Sgr’s pull over the past 150 Myr creates a global v z signature with amplitude ∝ M Sgr, which might be detectable in future spectroscopic surveys.