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arXiv 1407.4472astro-ph.GAastro-ph.CO
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大质量黑洞种子在各向异性Lyman-Werner源影响下的直接坍缩

The Direct Collapse of a Massive Black Hole Seed Under the Influence of an Anisotropic Lyman-Werner Source

John A. Regan, Peter H. Johansson, John H. Wise

摘要:

超大质量黑洞种子形成的直接坍缩模型为现在在$z \gtrsim 6$常规观测到的类星体的起源提供了一个有吸引力的解决方案。我们使用自适应网格加密程序Enzo模拟了高红移气体的坍缩,包括H,He和H $_2$的九种化学模型。直接坍缩模型要求气体主要通过氢原子冷却。为此,我们模拟的各向异性辐射源的高红移晕的崩溃的效果。辐射源放置在距离塌陷物体3 kpc(物理)的位置。光源设置为仅在$12.8 \ \rm{eV}$处的莱曼-沃纳(LW)带中心单色发射。利用射线追踪技术自洽地跟踪了高红移源发出的长波辐射。我们发现,由于自屏蔽,少量的H $_2$是能够形成在非常中心的坍缩晕,即使在非常强的LW辐射。此外,我们发现,需要一个辐射源,每秒发射$> 10^{54}\ (\sim10^3\ \rm{J_{21}})$光子,以引起$\rm{M \sim 10^5}$ M $_{\odot}$团的崩溃。坍缩天体的吸积率为$\sim 0.25$ M $_{\odot}$ $\rm{yr^{-1}}$。我们的结果显示显着的差异,相比各向同性辐射场的情况下,在H $_2$分数在等效半径。这些差异将显著影响崩溃的动力学。在强各向异性辐射源的作用下,坍缩物体的最终质量为$\rm{M \sim 10^5}$ M $_{\odot}$ .这与超大质量恒星或准恒星形成超大质量黑洞的预测是一致的。

英文摘要:

The direct collapse model of supermassive black hole seed formation provides an attractive solution to the origin of the quasars now routinely observed at $z \gtrsim 6$. We use the adaptive mesh refinement code Enzo to simulate the collapse of gas at high redshift, including a nine species chemical model of H, He, and H$_2$. The direct collapse model requires that the gas cools predominantly via atomic hydrogen. To this end we simulate the effect of an anisotropic radiation source on the collapse of a halo at high redshift. The radiation source is placed at a distance of 3 kpc (physical) from the collapsing object. The source is set to emit monochromatically in the center of the Lyman-Werner (LW) band only at $12.8 \ \rm{eV}$. The LW radiation emitted from the high redshift source is followed self-consistently using ray tracing techniques. We find that, due to self-shielding, a small amount of H$_2$ is able to form at the very center of the collapsing halo even under very strong LW radiation. Furthermore, we find that a radiation source, emitting $> 10^{54}\ (\sim10^3\ \rm{J_{21}})$ photons per second is required to cause the collapse of a clump of $\rm{M \sim 10^5}$ M$_{\odot}$. The resulting accretion rate onto the collapsing object is $\sim 0.25$ M$_{\odot}$ $\rm{yr^{-1}}$. Our results display significant differences, compared to the isotropic radiation field case, in terms of H$_2$ fraction at an equivalent radius. These differences will significantly effect the dynamics of the collapse. With the inclusion of a strong anisotropic radiation source, the final mass of the collapsing object is found to be $\rm{M \sim 10^5}$ M$_{\odot}$. This is consistent with predictions for the formation of a supermassive star or quasi-star leading to a supermassive black hole.

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