宇宙早期直接坍缩黑洞形成的新限制
New constraints on direct collapse black hole formation in the early Universe
摘要：
直接坍缩黑洞（DCBH）是$z>6$提出的一种解决超大质量黑洞组装问题的方法，用于解释这一时期观测到的明亮类星体。具有$\rm M_{BH}\sim10^{4-5}\ \rm M_{\odot}$的DCBH晶种的形成需要由足够强以完全抑制晕中的H $_{2}$冷却的外部辐射场照射原始原子冷却晕。许多以前的研究试图限制抑制H $_{2}$冷却可能需要的临界比强度，表示为$J_{\rm crit}$。然而，这些研究通常假设入射的外部辐射场可以用黑体光谱来建模。在此假设下，可以导出仅取决于黑体温度的$J_{\rm crit}$的{唯一}值。在这项研究中，我们认为一个更现实的光谱能量分布（SED）的外部辐射源，完全取决于它的恒星形成历史和年龄。负责抑制分子氢冷却的物种的破坏速率取决于SED的详细形状。因此，$J_{\rm crit}$的值与邻近星系入射SED的形状有关。我们拟合一个参数形式的破坏率的H $_2$和H $^-$，允许直接崩溃。由于这一点，我们发现$J_{\rm crit}$不是一个固定的阈值，但可以位于范围$J_{\rm crit} \sim 0.5$ -$10^{3}$的任何地方，这取决于源恒星人口的细节。
英文摘要：
Direct collapse black holes (DCBH) have been proposed as a solution to the challenge of assembling supermassive black holes by $z>6$ to explain the bright quasars observed at this epoch. The formation of a DCBH seed with $\rm M_{BH}\sim10^{4-5}\ \rm M_{\odot}$ requires a pristine atomic-cooling halo to be illuminated by an external radiation field that is sufficiently strong to entirely suppress H$_{2}$ cooling in the halo. Many previous studies have attempted to constrain the critical specific intensity that is likely required to suppress H$_{2}$ cooling, denoted as $J_{\rm crit}$. However, these studies have typically assumed that the incident external radiation field can be modeled with a black-body spectrum. Under this assumption, it is possible to derive a {unique} value for $J_{\rm crit}$ that depends only on the temperature of the black-body. In this study we consider a more realistic spectral energy distribution (SED) for the external source of radiation that depends entirely on its star formation history and age. The rate of destruction of the species responsible for suppressing molecular hydrogen cooling depends on the detailed shape of the SED. Therefore the value of $J_{\rm crit}$ is tied to the shape of the incident SED of the neighbouring galaxy. We fit a parametric form to the rates of destruction of H$_2$ and H$^-$ that permit direct collapse. Owing to this, we find that $J_{\rm crit}$ is not a fixed threshold but can lie anywhere in the range $J_{\rm crit} \sim 0.5$--$10^{3}$, depending on the details of the source stellar population.
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