不均匀金属混合对恒星考古学的意义
Implications of inhomogeneous metal mixing for stellar archaeology
摘要：
第一颗超新星用金属丰富了以前原始的气体，下一代恒星由此形成。基于流体动力学模拟，我们发展了一个新的随机模型来预测第一星系中恒星形成气体的金属丰度。平均而言，在内部富集的星系中，金属与原始气体混合良好。然而，在外部富集的星系中，金属不能轻易地渗透到致密气体中，这使得恒星形成气体和晕内的平均气体之间存在显着的金属丰度差异。为了研究这种效应的后果，我们应用半解析模型银河系般的暗物质合并树，并遵循恒星化石从高红移到今天的一个新的现实的金属混合配方。我们校准模型，以重现金属丰度分布函数（PMM）在低金属丰度，并发现一个原始的IMF与$\mathrm{d}N/\mathrm{d}M \propto M^{-0.5}$从$2 Msun$到$180 Msun$的斜率最好地再现PMM。我们改进的非均匀混合模型对单个微晕有很大的影响，但对[Fe/H] $\gtrsim -4$或最佳拟合Pop~III IMF的模拟结果没有显著影响。
英文摘要：
The first supernovae enrich the previously pristine gas with metals, out of which the next generation of stars form. Based on hydrodynamical simulations, we develop a new stochastic model to predict the metallicity of star-forming gas in the first galaxies. On average, in internally enriched galaxies, the metals are well mixed with the pristine gas. However, in externally enriched galaxies, the metals can not easily penetrate into the dense gas, which yields a significant metallicity difference between the star-forming and average gas inside a halo. To study the consequences of this effect, we apply a semi-analytical model to Milky Way-like dark matter merger trees and follow stellar fossils from high redshift until the present day with a novel realistic metal mixing recipe. We calibrate the model to reproduce the metallicity distribution function (MDF) at low metallicities and find that a primordial IMF with slope of $\mathrm{d}N/\mathrm{d}M \propto M^{-0.5}$ from $2 Msun$ to $180 Msun$ best reproduces the MDF. Our improved model for inhomogeneous mixing can have a large impact for individual minihalos, but does not significantly influence the modelled MDF at [Fe/H]$\gtrsim -4$ or the best-fitting Pop~III IMF.
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