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arXiv 0809.3752astro-ph
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通过云-云碰撞模拟银河系中心恒星盘的形成

Simulations of the formation of stellar discs in the Galactic centre via cloud-cloud collisions

Alexander Hobbs, Sergei Nayakshin

备注：
18 pages, 14 figures. Accepted for publication in MNRAS. Minor additions at referee request. Movies of simulations available at http://www.astro.le.ac.uk/~aph11/movies.html
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摘要：

我们银河系中央秒差距的年轻大质量恒星最好的解释是，恒星形成在至少一个，也可能是两个大质量自引力气体盘中。借助数值模拟，我们在这里考虑是否观察到的人口的年轻恒星可能起源于一个大角度碰撞的两个巨大的气体云在R约。距离Sgr A* 1秒差距。在所有的模拟中，碰撞后的气流形成了一个内部的，近圆形的气体盘和一个或两个偏心的外部细丝，与观察一致。此外，恒星质量的径向分布总是非常陡峭，σ与R^-2成正比，这也与观测结果一致。我们所有的模拟都产生了30到60度之间扭曲的圆盘，与最近的观测结果一致。恒星分布的3D速度结构对初始条件敏感（例如，云的碰撞参量）和气体冷却细节。例如，在运行中，内盘被间歇性地喂入具有波动角动量的物质，导致多个恒星盘具有不同的轨道取向，与观测数据相矛盾。在所有情况下，由我们的内边界条件吸积的气体量都很大，足以让Sgr A* 在其爱丁顿极限附近辐射大约1000次。10^5年。这表明，一个精确的模型将有物理上更大的云（或云和盘，如环核盘）在几个秒差距的距离碰撞，而不是像我们的模拟中的1秒差距。

英文摘要：

Young massive stars in the central parsec of our Galaxy are best explained by star formation within at least one, and possibly two, massive self-gravitating gaseous discs. With help of numerical simulations, we here consider whether the observed population of young stars could have originated from a large angle collision of two massive gaseous clouds at R approx. 1 parsec from Sgr A*. In all the simulations performed, the post-collision gas flow forms an inner, nearly circular gaseous disc and one or two eccentric outer filaments, consistent with the observations. Furthermore, the radial stellar mass distribution is always very steep, Sigma proportional to R^-2, again consistent with the observations. All of our simulations produce discs that are warped by between 30 to 60 degrees, in accordance with the most recent observations. The 3D velocity structure of the stellar distribution is sensitive to initial conditions (e.g., the impact parameter of the clouds) and gas cooling details. For example, the runs in which the inner disc is fed intermittently with material possessing fluctuating angular momentum result in multiple stellar discs with different orbital orientations, contradicting the observed data. In all the cases the amount of gas accreted by our inner boundary condition is large, enough to allow Sgr A* to radiate near its Eddington limit over approx. 10^5 years. This suggests that a refined model would have physically larger clouds (or a cloud and a disc such as the circumnuclear disc) colliding at a distance of a few parsecs rather than 1 parsec as in our simulations.

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