一个缓慢变平的银河系恒星盘：通过疏散星团的动力学轨道倾角研究银河系翘曲
A Slowly Flattening Milky Way Stellar Disk: Investigating Galactic Warping through Dynamical Orbital Inclinations of Open Clusters
AI总结：
本文利用疏散星团的动力学轨道倾角研究银河系翘曲，发现局部银盘倾斜导致此前翘曲进动速率被高估，并揭示银河系翘曲正在逐渐变平。
摘要：
通过评估不同银心半径处疏散星团（OC）样本的角动量方向，我们评估了它们的轨道平面倾角。我们的研究结果表明，在不考虑太阳附近银盘局部倾斜的情况下，我们的结果与之前对经典造父变星（CC）的研究一致。值得注意的是，由疏散星团推导出的翘曲进动与经典造父变星的结果高度吻合。尽管如此，我们观察到几何翘曲与动力学翘曲之间存在系统性偏差，这可归因于局部银盘的倾斜。我们在太阳邻域附近识别出与翘曲特征相关的系统性垂直运动。忽略这一运动会低估轨道平面倾角，与由几何位置推导出的倾角相比偏低。我们的研究表明，当太阳相对于银道中面的垂直速度为 Vz_sun = 9.4(0.2) km/s 时，由轨道动力学推导出的倾角与由几何位置推导出的倾角一致。这一数值比历史上估计的太阳本动速度 W_sun 高约 2 km/s，主要原因是局部平面存在约 0.6 度的倾斜。分析表明，此前对银河系银盘翘曲进动速率的估计可能因局部翘曲影响而被高估。研究结果表明，进动在零附近振荡，银河系翘曲正在逐渐变平。此外，在 1 亿至 2 亿年的时间尺度上，不同银心半径处的交点线趋于一致。
英文摘要：
By evaluating angular momentum directions of open cluster (OC) samples across various Galactocentric radii, we assessed their orbital plane inclinations. Our findings reveal that, without considering the local tilt of the Galactic disk near the sun, our results are consistent with previous studies on Classical Cepheids (CCs). Notably, the warp precession derived from OCs closely mirror those of CCs. Nonetheless, we observed a systematic deviation between the geometric and dynamic warps, attributable to the tilt of the local disk. We identified a systematic vertical motion in the local region, associated with the warping feature near the solar vicinity. Ignoring this motion leads to underestimates of orbital plane inclinations compared to those derived from geometric positions. Our study indicates consistency between the inclinations derived from orbital dynamics and geometric positions at a vertical velocity of the sun relative to the Galactic mid-plane of Vz_sun = 9.4(0.2) km/s. This value is approximately 2 km/s higher than the historically estimated solar peculiar motion, W_sun, primarily due to an approximately 0.6-degree tilt of the local plane. Analysis suggests that previous estimates of the Galactic disk's warping precession rate may have been overestimated due to local warping influences. The findings indicate that the precession oscillates around zero and that the Galactic warp is progressively flattening. Additionally, the line of nodes tends to become consistent across various Galactocentric radii over a timescale of 100-200 million years.
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