Understanding the evolution of self-gravitating, isothermal, magnetized gas is crucial for star formation, as these physical processes have been postulated to set the initial mass function (IMF). We present a suite of isothermal magnetohydrodynamic (MHD) simulations using the GIZMO code, that resolve the formation of individual stars in giant molecular clouds (GMCs), spanning a range of Mach numbers found in observed GMCs. As in past works, the mean and median stellar masses are sensitive to numerical resolution, because they are sensitive to low-mass stars that contribute a vanishing fraction of the overall stellar mass. The {\em mass-weighted} median stellar mass $M_\mathrm{50}$ becomes insensitive to resolution once turbulent fragmentation is well-resolved. Without imposing Larson-like scaling laws, our simulations find $M_\mathrm{50} \propto M_\mathrm{0} \mathcal{M}^{-3} \alpha_\mathrm{turb} \mathrm{SFE}^{1/3}$ for GMC mass $M_\mathrm{0}$, sonic Mach number $\mathcal{M}$, virial parameter $\alpha_\mathrm{turb}$, and star formation efficiency $\mathrm{SFE}=M_\mathrm{\star}/M_\mathrm{0}$. This fit agrees well with previous IMF results from the RAMSES, ORION2, and SphNG codes. Although $M_\mathrm{50}$ has no significant dependence on the magnetic field strength at the cloud scale, MHD is necessary to prevent a fragmentation cascade that results in non-convergent stellar masses. For initial conditions and SFE similar to star-forming GMCs in our Galaxy, we predict $M_\mathrm{50}$ to be $>20 M_{\odot}$, an order of magnitude larger than observed ($\sim 2 M_\odot$), together with an excess of brown dwarfs. Moreover, $M_\mathrm{50}$ is sensitive to initial cloud properties and evolves strongly in time within a given cloud, predicting much larger IMF variations than are observationally allowed. We conclude that physics beyond MHD turbulence and gravity are necessary ingredients for the IMF.

中文翻译：

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磁化湍流可以设置恒星的质量尺度吗？

了解自引力、等温、磁化气体的演化对于恒星的形成至关重要，因为这些物理过程已被假定为设置初始质量函数 (IMF)。我们使用 GIZMO 代码提供了一套等温磁流体动力学 (MHD) 模拟，该模拟解决了巨分子云 (GMC) 中单个恒星的形成问题，涵盖了在观测到的 GMC 中发现的一系列马赫数。与过去的工作一样，平均和中值恒星质量对数值分辨率很敏感，因为它们对低质量恒星敏感，而低质量恒星对整个恒星质量的贡献很小。{\em mass-weighted} 恒星质量中值 $M_\mathrm{50}$ 一旦湍流碎裂得到很好的解决就变得对分辨率不敏感。不施加类似拉森的缩放定律，我们的模拟发现 $M_\mathrm{50} \propto M_\mathrm{0} \mathcal{M}^{-3} \alpha_\mathrm{turb} \mathrm{SFE}^{1/3}$ 为 GMC 质量$M_\mathrm{0}$、声波马赫数$\mathcal{M}$、维里参数$\alpha_\mathrm{turb}$、恒星形成效率$\mathrm{SFE}=M_\mathrm{\star} /M_\mathrm{0}$. 这种拟合与之前来自 RAMSES、ORION2 和 SphNG 代码的 IMF 结果非常吻合。尽管 $M_\mathrm{50}$ 在云尺度上对磁场强度没有显着依赖性，但 MHD 是必要的，以防止导致非会聚恒星质量的碎裂级联。对于类似于我们银河系中恒星形成 GMC 的初始条件和 SFE，我们预测 $M_\mathrm{50}$ 为 $>20 M_{\odot}$，比观察到的 ($\sim 2 M_ \odot$)，以及过多的褐矮星。而且，$M_\mathrm{50}$ 对初始云属性很敏感，并且在给定的云中随时间变化强烈，预测的 IMF 变化比观测允许的大得多。我们得出结论，超越 MHD 湍流和引力的物理学是 IMF 的必要成分。