arXiv 1506.047502015-06-30astro-ph.GAastro-ph.HE

高红移黑洞的生长效率

The Growth Efficiency of High-Redshift Black Holes

Fabio Pacucci, Marta Volonteri, Andrea Ferrara

备注：: Accepted for publication in MNRAS
发表信息：: Monthly Notices of the Royal Astronomical Society 2015 452 (2): 1922-1933
DOI：: 10.1093/mnras/stv1465

摘要：

观测证据表明，超大质量黑洞（$M_{\bullet} \sim 10^{9-10} \, \mathrm{M_{\odot}}$）在大爆炸之后就已经存在了，这对它们的种子的生长效率提出了严格的时间限制。在提出的可能性中，大规模（$\sim 10^{3-6} \, \mathrm{M_{\odot}}$）种子的形成和/或超级爱丁顿（$\dot{M}>\dot{M}_{Edd}$）吸积事件的发生可能有助于解决这个问题。在这项工作中，我们分析和数值研究高红移（$z \sim 10$）黑洞的吸积流，以了解有利于快速和有效增长的物理要求。我们的模型确定了一个“喂养为主”的吸积制度和一个“反馈有限”，后者的特点是间歇性（占空比${\cal D} \lesssim 0.5$）和低效的增长，与经常性的外流事件。我们发现，低质量的种子（$\lesssim 10^{3-4} \, \mathrm{M_{\odot}}$）进化的反馈限制制度，而更大规模的种子（$\gtrsim 10^{5-6} \, \mathrm{M_{\odot}}$）生长非常迅速，因为它们被发现在喂养为主的制度。除了具有固定的物质能量转换因子的标准吸积模型（$ε= 0.1$）之外，我们还探索了适合于超爱丁顿吸积的细长盘模型，其中辐射被捕获在盘中并且辐射效率降低（$ε\lesssim 0.04$），这可以确保$\dot{M} \gg \dot{M}_{Edd}$的连续增长（在我们的模拟中高达$\sim 300\dot{M}_{Edd}$）。在这些条件下，流出发挥了微不足道的作用，黑洞可以吸积的气体质量的主机晕（$\sim 10^7 \, \mathrm{M_{\odot}}$）在$\sim 10 \, \mathrm{Myr}$的$80\%-100\%$，而在反馈有限的系统中，我们预测，黑洞可以吸积只有$\sim 15\%$的可用质量。

英文摘要：

The observational evidence that Super-Massive Black Holes ($M_{\bullet} \sim 10^{9-10} \, \mathrm{M_{\odot}}$) are already in place less than $1 \, \mathrm{Gyr}$ after the Big Bang poses stringent time constraints on the growth efficiency of their seeds. Among proposed possibilities, the formation of massive ($\sim 10^{3-6} \, \mathrm{M_{\odot}}$) seeds and/or the occurrence of super-Eddington ($\dot{M}>\dot{M}_{Edd}$) accretion episodes may contribute to the solution of this problem. In this work we analytically and numerically investigate the accretion flow onto high-redshift ($z \sim 10$) black holes to understand the physical requirements favoring rapid and efficient growth. Our model identifies a "feeding-dominated" accretion regime and a "feedback-limited" one, the latter being characterized by intermittent (duty cycles ${\cal D} \lesssim 0.5$) and inefficient growth, with recurring outflow episodes. We find that low-mass seeds ($\lesssim 10^{3-4} \, \mathrm{M_{\odot}}$) evolve in the feedback-limited regime, while more massive seeds ($\gtrsim 10^{5-6} \, \mathrm{M_{\odot}}$) grow very rapidly as they are found in the feeding-dominated regime. In addition to the standard accretion model with a fixed matter-energy conversion factor ($ε= 0.1$), we have also explored slim disk models, appropriate for super-Eddington accretion, where radiation is trapped in the disk and the radiative efficiency is reduced ($ε\lesssim 0.04$), which may ensure a continuous growth with $\dot{M} \gg \dot{M}_{Edd}$ (up to $\sim 300\dot{M}_{Edd}$ in our simulations). Under these conditions, outflows play a negligible role and a black hole can accrete $80\%-100\%$ of the gas mass of the host halo ($\sim 10^7 \, \mathrm{M_{\odot}}$) in $\sim 10 \, \mathrm{Myr}$, while in feedback-limited systems we predict that black holes can accrete only up to $\sim 15\%$ of the available mass.

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