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arXiv 1909.07548astro-ph.GA
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用核星盘测定银河棒的年龄

Age Dating the Galactic Bar with the Nuclear Stellar Disc

Junichi Baba, Daisuke Kawata

备注：
accepted for publication in MNRAS
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摘要：

几十年来的理论研究表明，棒的形成触发了气体向中心亚千秒差距区域的汇集，并导致了运动学冷核星盘（NSD）的形成。我们证明，这种机制可以用来识别银河系酒吧的形成时代，使用一个孤立的银河系类星系的N体/流体动力学模拟。正如许多以前的文献中所示，我们的模拟表明，酒吧的形成触发了强烈的恒星形成的~1 Gyr在中央区域，并形成一个NSD。因此，NSD的最老年龄限制相对尖锐，最老人口变得与酒吧的年龄相似。因此，NSD的年龄分布告诉我们砂坝的形成时代。我们讨论的一个主要挑战，在测量银河系中的NSD的年龄分布是污染的其他不可忽略的恒星组件在中央区域，如一个经典的凸起组件。我们证明，由于NSD是运动学冷比其他恒星星族在银河系中心区域，NSD人口可以从其他恒星星族运动学区分，如果示踪星的三维速度被精确测量。因此，除了从光谱测量的视线速度，恒星的横向速度的准确测量是必要的，因此，近红外空间天体测量任务，JASMINE，将发挥关键作用，以确定银河酒吧的形成时代。我们还讨论了恒星年龄估计的准确性对测量NSD恒星星族的最老极限也是至关重要的。

英文摘要：

From the decades of the theoretical studies, it is well known that the formation of the bar triggers the gas funnelling into the central sub-kpc region and leads to the formation of a kinematically cold nuclear stellar disc (NSD). We demonstrate that this mechanism can be used to identify the formation epoch of the Galactic bar, using an N-body/hydrodynamics simulation of an isolated Milky Way-like galaxy. As shown in many previous literature, our simulation shows that the bar formation triggers an intense star formation for ~1 Gyr in the central region, and forms a NSD. As a result, the oldest age limit of the NSD is relatively sharp, and the oldest population becomes similar to the age of the bar. Therefore, the age distribution of the NSD tells us the formation epoch of the bar. We discuss that a major challenge in measuring the age distribution of the NSD in the Milky Way is contamination from other non-negligible stellar components in the central region, such as a classical bulge component. We demonstrate that because the NSD is kinematically colder than the other stellar populations in the Galactic central region, the NSD population can be kinematically distinguished from the other stellar populations, if the 3D velocity of tracer stars are accurately measured. Hence, in addition to the line-of-sight velocities from spectroscopic surveys, the accurate measurements of the transverse velocities of stars are necessary, and hence the near-infrared space astrometry mission, JASMINE, would play a crutial role to identify the formation epoch of the Galactic bar. We also discuss that the accuracy of stellar age estimation is also crucial to measure the oldest limit of the NSD stellar population.

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