通过碰撞逃逸在原始星团中播种高红移类星体
Seeding High Redshift QSOs by Collisional Runaway in Primordial Star Clusters
摘要：
我们研究如何失控的恒星碰撞高红移，贫金属星团形成非常大质量的恒星（VMSs），可以直接崩溃到中等质量的黑洞（IMBHs）。我们遵循一对相邻的高红移迷你晕的演化与高分辨率，宇宙学流体动力学放大模拟使用自适应网格细化代码RAMSES结合非平衡化学包KROME。第一个坍缩的小晕被认为是将另一个的中央核星团（NSC）富集到临界金属丰度，足以形成红移为$z\approx27$的星族II（Pop. II）恒星。使用的空间配置的扁平，不对称的气体云形成的核心的金属富集晕，我们设置的初始条件，模拟一个最初的非球形星团的直接求和代码NBODY6相比，约2000 NBODY6模拟球形星团的广泛的星团参数。最终形成的VMS的质量很大程度上取决于NSC的初始质量和初始中心密度。对于我们的RAMSES模拟建议的初始中心密度，质量> 400 M $_{\odot}$的VMS可以在恒星质量为$\approx10^4$ M $_{\odot}$的星团中形成，并且对于更大质量和更密集的星团，这可以增加到远超过1000 M $_{\odot}$。我们发现在这样一个早期的宇宙时间在这些小晕中形成VMS的概率很高，这使得Pop.II星团的碰撞失控成为产生大量高红移IMBH的一个有希望的通道，这些IMBH可能作为超大质量黑洞的种子。
英文摘要：
We study how runaway stellar collisions in high-redshift, metal-poor star clusters form very massive stars (VMSs) that can directly collapse to intermediate-mass black holes (IMBHs). We follow the evolution of a pair of neighbouring high-redshift mini-haloes with high-resolution, cosmological hydrodynamical zoom-in simulations using the adaptive mesh refinement code RAMSES combined with the non-equilibrium chemistry package KROME. The first collapsing mini-halo is assumed to enrich the central nuclear star cluster (NSC) of the other to a critical metallicity, sufficient for Population II (Pop. II) star formation at redshift $z\approx27$. Using the spatial configuration of the flattened, asymmetrical gas cloud forming in the core of the metal enriched halo, we set the initial conditions for simulations of an initially non-spherical star cluster with the direct summation code NBODY6 which are compared to about 2000 NBODY6 simulations of spherical star clusters for a wide range of star cluster parameters. The final mass of the VMS that forms depends strongly on the initial mass and initial central density of the NSC. For the initial central densities suggested by our RAMSES simulations, VMSs with mass > 400 M$_{\odot}$ can form in clusters with stellar masses of $\approx10^4$ M$_{\odot}$, and this can increase to well over 1000 M$_{\odot}$ for more massive and denser clusters. The high probability we find for forming a VMS in these mini-haloes at such an early cosmic time makes collisional runaway of Pop. II star clusters a promising channel for producing large numbers of high-redshift IMBHs that may act as the seeds of supermassive black holes.
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