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arXiv 1710.09375astro-ph.GAastro-ph.COastro-ph.HE
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黑洞种子最优生长的条件

Conditions for Optimal Growth of Black Hole Seeds

Fabio Pacucci, Priyamvada Natarajan, Marta Volonteri, Nico Cappelluti, C. Megan Urry

摘要:

当宇宙的年龄为$\lesssim 1 \, \mathrm{Gyr}$时,重量高达$\sim 10^9 \, \mathrm{M_{\odot}}$的超大质量黑洞在$z \sim 7$的位置。这意味着它们的生长时间紧迫,因为在标准的吸积情景中不容易达到如此高的质量。在这里,我们探讨的物理条件,将导致最佳的增长,其中稳定的超爱丁顿吸积将被允许。我们的分析表明,最佳条件的优势取决于两个关键参数:黑洞质量和宿主星系中心气体密度。在这个参数空间的高效率区域,假设宿主星系具有全球等温分布,一股连续的气流可以从大到小的空间尺度吸积到黑洞上。利用黑洞种子的解析初始质量函数,我们发现初始质量为$\gtrsim 10^4 \, \mathrm{M_{\odot}}$的种子的高效率增长的概率增加。我们的图像表明,在低效率区域形成的大量高$z$低质量黑洞,具有低占空比和吸积率,可能仍然无法检测到类星体,因为我们预测它们的热光度为$\lesssim 10^{41} \, \mathrm{erg \, s^{-1}}$。只有通过引力波探测它们的合并,才能揭示这些源的存在。

英文摘要:

Super-massive black holes weighing up to $\sim 10^9 \, \mathrm{M_{\odot}}$ are in place by $z \sim 7$, when the age of the Universe is $\lesssim 1 \, \mathrm{Gyr}$. This implies a time crunch for their growth, since such high masses cannot be easily reached in standard accretion scenarios. Here, we explore the physical conditions that would lead to optimal growth wherein stable super-Eddington accretion would be permitted. Our analysis suggests that the preponderance of optimal conditions depends on two key parameters: the black hole mass and the host galaxy central gas density. In the high-efficiency region of this parameter space, a continuous stream of gas can accrete onto the black hole from large to small spatial scales, assuming a global isothermal profile for the host galaxy. Using analytical initial mass functions for black hole seeds, we find an enhanced probability of high-efficiency growth for seeds with initial masses $\gtrsim 10^4 \, \mathrm{M_{\odot}}$. Our picture suggests that a large population of high-$z$ lower-mass black holes that formed in the low-efficiency region, with low duty cycles and accretion rates, might remain undetectable as quasars, since we predict their bolometric luminosities to be $\lesssim 10^{41} \, \mathrm{erg \, s^{-1}}$. The presence of these sources might be revealed only via gravitational wave detections of their mergers.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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