直接坍缩黑洞形成的短暂时代
The brief era of direct collapse black hole formation
摘要：
有人提出，第一个中等质量（$\approx 10^{5-6}~M_\odot$）黑洞可能是通过暴露在强莱曼-沃纳（LW）或近红外（NIR）辐射下的原子冷却晕中的未污染气体直接坍缩形成的。由于这些系统预计具有康普顿厚度，因此13.6 eV以上的光子大部分被吸收并重新处理成较低的能带。因此，直接坍缩黑洞（DCBH）在LW/NIR波段非常明亮，通常比小型高红移星系亮10倍以上。一旦第一个DCBH形成，它们就会触发进一步形成DCBH的失控过程，使其宇宙质量密度突然上升。宇宙在$z \approx 20$进入“DCBH时代”，此时大部分原子冷却晕正在经历DCBH的形成。通过结合蒙特卡罗模拟的辐射源的聚类特性，我们表明，在这种情况下，DCBH的质量密度上升从$\sim 5$ ~ $M_\odot$ Mpc $^{-3}$在$z\sim 30$的峰值$\sim5\times10^5 M_\odot$ Mpc $^{-3}$在$z \sim 14$在我们的基准模型。然而，\textit{active}（吸积）DCBHs的丰度在$z \sim 14$之后下降，因为潜在形成地点（维里温度略高于$10^4$ ~K的未污染晕）中的气体被光蒸发。这种效应几乎完全抑制了$z\sim 13$后的DCBH形成。DCBH的形成时代只持续了$\approx 150$ Myr，但它可能是至关重要的超大质量黑洞（SMBH）的种子，为$z\sim6$类星体提供动力。
英文摘要：
It has been proposed that the first, intermediate-mass ($\approx 10^{5-6}~M_\odot$) black holes might form through direct collapse of unpolluted gas in atomic-cooling halos exposed to a strong Lyman-Werner (LW) or near-infrared (NIR) radiation. As these systems are expected to be Compton-thick, photons above 13.6 eV are largely absorbed and re-processed into lower energy bands. It follows that direct collapse black holes (DCBHs) are very bright in the LW/NIR bands, typically outshining small high-redshift galaxies by more than 10 times. Once the first DCBHs form, they then trigger a runaway process of further DCBH formation, producing a sudden rise in their cosmic mass density. The universe enters the "DCBH era" at $z \approx 20$ when a large fraction of atomic-cooling halos are experiencing DCBH formation. By combining the clustering properties of the radiation sources with Monte Carlo simulations we show that in this scenario the DCBH mass density rises from $\sim 5$~$M_\odot$ Mpc$^{-3}$ at $z\sim 30$ to the peak value $\sim5\times10^5 M_\odot$ Mpc$^{-3}$ at $z \sim 14$ in our fiducial model. However, the abundance of \textit{active} (accreting) DCBHs drops after $z \sim 14$, as gas in the potential formation sites (unpolluted halos with virial temperature slightly above $10^4$~K) is photoevaporated. This effect almost completely suppresses DCBH formation after $z\sim 13$. The DCBH formation era lasts only $\approx 150$ Myr, but it might crucially provide the seeds of the supermassive black holes (SMBHs) powering $z\sim6$ quasars.
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