Population III stars are believed to have been more massive than typical stars today and to have formed in relative isolation. The thermodynamic impact of metals is expected to induce a transition leading to clustered, low-mass Population II star formation. In this work, we present results from three cosmological simulations, only differing in gas metallicity, that focus on the impact of metal fine-structure line cooling on the formation of stellar clusters in a high-redshift atomic cooling halo. Introduction of sink particles allows us to follow the process of gas hydrodynamics and accretion onto cluster stars for 4 Myr corresponding to multiple local free-fall times. At metallicities at least $10^{-3}\, Z_{\odot}$, gas is able to reach the CMB temperature floor and fragment pervasively resulting in a stellar cluster of size $\sim1$ pc and total mass $\sim1000\, M_{\odot}$. The masses of individual sink particles vary, but are typically $\sim100\, M_{\odot}$, consistent with the Jeans mass when gas cools to the CMB temperature, though some solar mass fragments are also produced. At the low metallicity of $10^{-4}\, Z_{\odot}$, fragmentation is completely suppressed on scales greater than 0.01 pc and total stellar mass is lower by a factor of 3 than in the higher metallicity simulations. The sink particle accretion rates, and thus their masses, are determined by the mass of the gravitationally unstable gas cloud and the prolonged gas accretion over many Myr. The simulations thus exhibit features of both monolithic collapse and competitive accretion. Even considering possible dust induced fragmentation that would occur at higher densities, the formation of a bona fide stellar cluster seems to require metal line cooling and metallicities of at least $10^{-3}\, Z_{\odot}$.
The Enrichment of the Intergalactic Medium with Adiabatic Feedback I: Metal Cooling and Metal Diffusion
采用金属冷却、金属湍流扩散和热能，利用一系列SPH模拟研究IGM金属富集。采用绝热反馈机制，防止气体冷却，产生没有明确的风粒子的星系风。模拟产生的宇宙恒星形成历史（SFH）与观测结果大致一致，直到z $\sim$ 0.5，以及通用中性氢分数（$Ω_{\rm H I}$）的稳定演变。在z=0时，大约40%的重子在温暖的星系际介质（WHIM）中，但大多数金属（80%-90%）被锁定在恒星中。在较高的z，IGM中的金属比例较高，这是由于星系更有效的损失。在整个宇宙历史中，IGM金属主要存在于WHIM。星系内部气体的金属丰度演化与观测结果基本一致，但弥散IGM在z $\sim$ 2.5处富集。银河风最有效地富集了中等质量范围$10^{10}$ M $_{\sun}$ - $10^{11}$ M $_{\sun}$的晕的IGM。在低质量端气体被阻止吸积到晕上，并且具有非常低的金属丰度。在高质量端，随着星系中恒星质量分数的降低，晕重子逃逸率也随之降低。这可能是因为恒星形成活动和逃逸效率的降低。金属增强冷却，使WHIM气体冷却到星系上，并增加恒星的形成。金属的扩散使得风在逃逸之前混合，减少了IGM的金属含量，有利于星系晕内的气体和恒星形成气体。扩散显著增加了低金属丰度气体的量，并改变了密度-金属丰度关系。
On The Road To More Realistic Galaxy Cluster Simulations: The Effects of Radiative Cooling and Thermal Feedback Prescriptions on the Observational Properties of Simulated Galaxy Clusters
Hot versus Cold: the Dichotomy in Spherical Accretion of Cooling Flows onto Supermassive Black Holes in Elliptical Galaxies, Galaxy Groups and Clusters
