A supersonic cloud-cloud collision produces a shock-compressed layer which leads to formation of high-mass stars via gravitational instability. We carried out a detailed analysis of the layer by using the numerical simulations of magneto-hydrodynamics which deal with colliding molecular flows at a relative velocity of 20 km s$^{-1}$ (Inoue & Fukui 2013). Maximum density in the layer increases from 1000 cm$^{-3}$ to more than $10^{5}$ cm$^{-3}$ within 0.3 Myrs by compression, and the turbulence and the magnetic field in the layer are amplified by a factor of $\sim 5$, increasing the mass accretion rate by two orders of magnitude to more than $10^{-4}$ $M_{\odot}$ yr$^{-1}$. The layer becomes highly filamentary due to gas flows along the magnetic field lines, and dense cores are formed in the filaments. The massive dense cores have size and mass of 0.03 -- 0.8 pc and 8 -- 50 $M_{\odot}$ and they are usually gravitationally unstable. The mass function of the dense cores is significantly top-heavy as compared with the universal IMF, indicating that the cloud-cloud collision triggers preferentially the formation of O and early B stars. We argue that the cloud-cloud collision is a versatile mechanism which creates a variety of stellar clusters from a single O star like RCW120 and M20 to tens of O stars of a super star cluster like RCW38 and a mini-starburst W43. The core mass function predicted by the present model is consistent with the massive dense cores obtained by recent ALMA observations in RCW38 (Torii et al. 2019) and W43 (Motte et al. 2018) considering the increasing evidence for collision-triggered high-mass star formation, we argue that cloud-cloud collision is a major mechanism of high mass star formation.

中文翻译：

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通过超音速云-云碰撞快速有效地收集质量作为大质量恒星形成的主要机制

超音速云云碰撞会产生一个冲击压缩层，通过引力不稳定性导致大质量恒星的形成。我们通过使用磁流体动力学的数值模拟对该层进行了详细分析，该模拟处理以 20 公里 s$^{-1}$ 的相对速度碰撞分子流（Inoue & Fukui 2013）。层中的最大密度通过压缩从 1000 cm$^{-3}$ 增加到超过 $10^{5}$ cm$^{-3}$ 0.3 Myrs 内，并且层中的湍流和磁场为放大了 $\sim 5$ 倍，使质量吸积率增加了两个数量级，超过 $10^{-4}$ $M_{\odot}$ yr$^{-1}$。由于气体沿着磁场线流动，该层变得高度丝状，并且在细丝中形成致密的核。大质量致密核心的大小和质量为 0.03 -- 0.8 pc 和 8 -- 50 $M_{\odot}$，它们通常在重力上不稳定。与普遍的 IMF 相比，致密核心的质量函数明显是头重脚轻的，表明云-云碰撞优先触发 O 星和早期 B 星的形成。我们认为云-云碰撞是一种多功能的机制，它产生了从像 RCW120 和 M20 这样的单个 O 星到像 RCW38 和迷你星暴 W43 这样的超级星团的数十个 O 星的各种星团。本模型预测的核心质量函数与最近 ALMA 在 RCW38 (Torii et al. 2019) 和 W43 (Motte et al. 2018) 中观测获得的大质量致密核心一致，考虑到越来越多的证据表明碰撞触发的大质量恒星形成，