SIRIUS project. I. Star formation models for star-by-star simulations of star clusters and galaxy formation
SIRIUS project. I. Star formation models for star-by-star simulations of star clusters and galaxy formation
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DOI：
10.1093/pasj/psab038
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发表时间：
2020-05
影响因子：
2.3
通讯作者：
Y. Hirai;M. Fujii;T. Saitoh
中科院分区：
文献类型：
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作者：
Y. Hirai;M. Fujii;T. Saitoh
大多数恒星在星系中形成为星星团，然后分散成星系盘。即将到来的艾级超级计算设施将能够通过解析单个恒星来模拟星系及其形成（逐星星模拟）。这将大大推进我们对星系中星星形成、星星团形成和星系聚集历史的理解。在以前的星系模拟中，使用了简单的恒星人口近似。然而，很难用这种近似来提高质量分辨率。因此，必须建立一个可以用于模拟星系的单个恒星形成模型。本文是SIRIUS（SIMULATIONS RESOLVING INDIDUUAL STARS）项目系列的第一篇论文，我们展示了一个用于逐颗星星模拟的随机星星形成模型。在这个模型中，一个假定的恒星初始质量函数（IMF）被随机分配给新形成的恒星。我们引入了最大搜索半径来聚集周围气体粒子的质量以形成星星粒子。在这项研究中，我们进行了一系列的N体/光滑粒子流体动力学模拟的星星集群的形成从湍流分子云和超微弱的矮星系作为测试用例。如果采用大于由星星形成的阈值密度估计的最大搜索半径，则IMF可以被正确地采样。在小星云中，大质量恒星的形成是高度随机的，因为恒星的数量很少。我们证实，星星形成效率和阈值密度不会强烈影响结果。我们发现我们的模型可以自然地再现质量最大的恒星和星星团的总恒星质量之间的关系。在这里，我们表明，我们的模型可以适用于不同的模拟从星星集群星系的分辨率范围很广。
Most stars are formed as star clusters in galaxies, which then disperse into galactic disks. Upcoming exascale supercomputational facilities will enable simulations of galaxies and their formation by resolving individual stars (star-by-star simulations). This will substantially advance our understanding of star formation in galaxies, star cluster formation, and assembly histories of galaxies. In previous galaxy simulations, a simple stellar population approximation was used. It is, however, difficult to improve the mass resolution with this approximation. Therefore, a model for forming individual stars that can be used in simulations of galaxies must be established. In this first paper of a series from the SIRIUS (SImulations Resolving IndividUal Stars) project, we demonstrate a stochastic star formation model for star-by-star simulations. An assumed stellar initial mass function (IMF) is randomly assigned to newly formed stars in this model. We introduce a maximum search radius to assemble the mass from surrounding gas particles to form star particles. In this study, we perform a series of N-body/smoothed particle hydrodynamics simulations of star cluster formations from turbulent molecular clouds and ultra-faint dwarf galaxies as test cases. The IMF can be correctly sampled if a maximum search radius that is larger than the value estimated from the threshold density for star formation is adopted. In small clouds, the formation of massive stars is highly stochastic because of the small number of stars. We confirm that the star formation efficiency and threshold density do not strongly affect the results. We find that our model can naturally reproduce the relationship between the most massive stars and the total stellar mass of star clusters. Herein, we demonstrate that our models can be applied to simulations varying from star clusters to galaxies for a wide range of resolutions.