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SIRIUS project. I. Star formation models for star-by-star simulations of star clusters and galaxy formation
Publications of the Astronomical Society of Japan ( IF 2.3 ) Pub Date : 2021-04-22 , DOI: 10.1093/pasj/psab038
Yutaka Hirai 1, 2 , Michiko S Fujii 3 , Takayuki R Saitoh 4, 5
Affiliation  

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.

中文翻译:

天狼星项目。一、星团和星系形成逐星模拟的恒星形成模型

大多数恒星在星系中形成为星团,然后分散成星系盘。即将推出的百亿亿级超级计算设施将通过解析单个恒星(逐星模拟)来模拟星系及其形成。这将大大提高我们对星系中恒星形成、星团形成和星系组装历史的理解。在以前的星系模拟中,使用了简单的恒星种群近似值。然而,用这种近似值很难提高质量分辨率。因此,必须建立可用于模拟星系的单个恒星形成模型。在 SIRIUS(解决单个恒星的模拟)项目系列的第一篇论文中,我们展示了用于逐星模拟的随机恒星形成模型。在该模型中,假定的恒星初始质量函数 (IMF) 被随机分配给新形成的恒星。我们引入了一个最大搜索半径来将周围气体粒子的质量聚集起来形成星粒子。在这项研究中,我们对来自湍流分子云和超微弱矮星系的星团形成进行了一系列 N 体/平滑粒子流体动力学模拟作为测试用例。如果采用大于根据恒星形成阈值密度估计的值的最大搜索半径,则可以正确采样 IMF。在小云中,由于恒星数量少,大质量恒星的形成是高度随机的。我们确认恒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最大质量恒星与星团总恒星质量之间的关系。在这里,我们证明我们的模型可以应用于从星团到星系的各种分辨率的模拟。
更新日期:2021-04-22
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