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arXiv 1506.08196astro-ph.GA
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星系核气体云的稳定性:一个推广的维里定理

Stability of Gas Clouds in Galactic Nuclei: An Extended Virial Theorem

Xian Chen, Pau Amaro-Seoane, Jorge Cuadra

摘要:

进入星系中央$1$到$10^2$ pc的冷气体碎裂并凝结成云。云层的稳定性决定了它们是否会变成恒星,或者是否可以被输送到中央超大质量黑洞(SMBH)以打开活动星系核(AGN)。传统的标准来评估这些云的稳定性,如金斯标准和罗氏(或潮汐)限制,在这里是不够的,因为他们假设在绑定云的自引力的主导地位,并忽略了外部的代理商,如压力和潮汐力,这是常见的星系核。我们制定了一个新的方案来判断这种稳定性。我们首先回顾了传统的维里定理,考虑到外部压力,以确定正确的质量范围,导致稳定的云。然后,我们将定理扩展到包括外部潮汐场,这对感兴趣区域的稳定性至关重要-在密集的星团中,围绕SMBH。我们应用我们的扩展维里定理,找到正确的解决方案,到现在为止有争议的实际问题,即,在AGN环,在银河系中心的环核盘,和银河系的中央分子区的气体团块的稳定性。我们推导出的这些结构的质量比常用的维里质量(相当于金斯质量)小几个数量级。此外,我们证明,这些团块是稳定的,相反,人们会天真地推断出罗氏(潮汐)限制。

英文摘要:

Cold gas entering the central $1$ to $10^2$ pc of a galaxy fragments and condenses into clouds. The stability of the clouds determines whether they will be turned into stars or can be delivered to the central supermassive black hole (SMBH) to turn on an active galactic nucleus (AGN). The conventional criteria to assess the stability of these clouds, such as the Jeans criterion and Roche (or tidal) limit, are insufficient here, because they assume the dominance of self-gravity in binding a cloud, and neglect external agents, such as pressure and tidal forces, which are common in galactic nuclei. We formulate a new scheme for judging this stability. We first revisit the conventional Virial theorem, taking into account an external pressure, to identify the correct range of masses that lead to stable clouds. We then extend the theorem to include an external tidal field, crucial for the stability in the region of interest -- in dense star clusters, around SMBHs. We apply our extended Virial theorem to find the correct solutions to practical problems that until now were controversial, namely, the stability of the gas clumps in AGN tori, the circum-nuclear disk in the Galactic Center, and the central molecular zone of the Milky Way. The masses we derive for these structures are orders of magnitude smaller than the commonly-used Virial masses (equivalent to the Jeans mass). Moreover, we prove that these clumps are stable, contrary to what one would naively deduce from the Roche (tidal) limit.

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