H2self-shielding with non-LTE rovibrational populations: implications for cooling in protogalaxies
H2self-shielding with non-LTE rovibrational populations: implications for cooling in protogalaxies
复制标题
非 LTE 旋转群体的 H2 自屏蔽：对原星系冷却的影响
DOI：
10.1093/mnras/sty3280
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发表时间：
2018
影响因子：
4.8
通讯作者：
Z. Haiman
中科院分区：
文献类型：
--
作者：
J. Wolcott;Z. Haiman
原始气体中的主要冷却剂分子氢（H2）的丰度对于早期原星系的热力学演化和恒星形成历史至关重要。因此，通过入射莱曼-沃纳（LW）通量确定H2的光解速率是至关重要的，但在模拟中进行实时计算的成本过高。该速率对H2的振转分布敏感，而振转分布又取决于气体密度、温度和入射LW辐射场。我们使用公开可用的多云包来模拟原始气体云，并将精确的光解速率计算与常用的拟合公式进行比较。我们发现Wolcott-Green等人（2011）的拟合在中等密度n~10^3 cm^{-3}和温度T~ 10^3 K时最准确，我们提供了一个新的拟合，它捕捉到了更高密度和温度下速率的增加，这是由于在该区域激发的振转布居数增加。我们的新拟合在n = 10^3和n < 10^2 cm^{-3}时具有几个百分比的典型误差。这可能会降低一些原星系中原始气体保持H2贫乏的“临界通量”，从而使大质量黑洞种子形成。
The abundance of molecular hydrogen (H2), the primary coolant in primordial gas, is critical for the thermodynamic evolution and star-formation histories in early protogalaxies. Determining the photodissociation rate of H2 by an incident Lyman-Werner (LW) flux is thus crucial, but prohibitively expensive to calculate on the fly in simulations. The rate is sensitive to the H2 rovibrational distribution, which in turn depends on the gas density, temperature, and incident LW radiation field. We use the publicly available cloudy package to model primordial gas clouds and compare exact photodissociation rate calculations to commonly-used fitting formulae. We find the fit from Wolcott-Green et al. (2011) is most accurate for moderate densities n~10^3 cm^{-3} and temperatures, T~10^3K, and we provide a new fit, which captures the increase in the rate at higher densities and temperatures, owing to the increased excited rovibrational populations in this regime. Our new fit has typical errors of a few percent percent up to n = 10^3 and n < 10^2 cm^{-3}. This may lower the "critical flux" at which primordial gas remains H2-poor in some protogalaxies, enabling massive black hole seed formation.