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arXiv 1109.0986astro-ph.GA
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恒星形成区恒星结构的动力学状态

The dynamical state of stellar structure in star-forming regions

J. M. Diederik Kruijssen, Thomas Maschberger, Nickolas Moeckel, Cathie J. Clarke, Nate Bastian, Ian A. Bonnell

摘要:

恒星形成的分数,导致在恒星形成的密度谱和气体驱逐的恒星结构的反应的影响。我们分析流体动力学模拟的恒星形成区域的湍流碎片,以评估由此产生的人口的恒星和(子)集群的动力学特性。恒星子集群使用最小生成树算法进行识别。当只考虑恒星的引力势而忽略气体时,我们发现所识别的子团接近维里平衡(典型的维里比Q_vir~0.59,而维里平衡则为Q_vir~0.5)。这种维里态是由于气体吸积到恒星上,以及吸积引起的子星系团收缩,导致子星系团内气体比例较低的结果。由于子星系团是气体贫乏的,在模拟结束时的长度尺度为0.1-0.2 pc,它们只受到气体排出的微弱影响。子星系团达到高密度所需的演化到气体贫乏状态的比例随着恒星形成区域的密度而增加。我们将这一论点扩展到星团尺度,并认为气体的缺乏表明,由于气体排出(婴儿死亡率)导致的星团早期破坏比预期的作用要小,并且可能仅限于周围气体密度低的恒星形成区域。我们认为,在致密的恒星形成区域,周围气体云对年轻星团的潮汐冲击可能是早期破坏的原因。这种“残酷的摇篮效应”将在气体排出的破坏之外发挥作用。我们提出了可能的方法来量化这两种机制的相对贡献。

英文摘要:

The fraction of star formation that results in bound star clusters is influenced by the density spectrum in which stars are formed and by the response of the stellar structure to gas expulsion. We analyse hydrodynamical simulations of turbulent fragmentation in star-forming regions to assess the dynamical properties of the resulting population of stars and (sub)clusters. Stellar subclusters are identified using a minimum spanning tree algorithm. When considering only the gravitational potential of the stars and ignoring the gas, we find that the identified subclusters are close to virial equilibrium (the typical virial ratio Q_vir~0.59, where virial equilibrium would be Q_vir~0.5). This virial state is a consequence of the low gas fractions within the subclusters, caused by the accretion of gas onto the stars and the accretion-induced shrinkage of the subclusters. Because the subclusters are gas-poor, up to a length scale of 0.1-0.2 pc at the end of the simulation, they are only weakly affected by gas expulsion. The fraction of subclusters that reaches the high density required to evolve to a gas-poor state increases with the density of the star-forming region. We extend this argument to star cluster scales, and suggest that the absence of gas indicates that the early disruption of star clusters due to gas expulsion (infant mortality) plays a smaller role than anticipated, and is potentially restricted to star-forming regions with low ambient gas densities. We propose that in dense star-forming regions, the tidal shocking of young star clusters by the surrounding gas clouds could be responsible for the early disruption. This `cruel cradle effect' would work in addition to disruption by gas expulsion. We suggest possible methods to quantify the relative contributions of both mechanisms.

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