arXiv 1402.08822014-02astro-ph.CO

在含时Lyman-Werner背景下的高红移恒星形成

High-Redshift Star Formation in a Time-Dependent Lyman-Werner Background

Eli Visbal, Zoltan Haiman, Bryan Terrazas, Greg L. Bryan, Rennan Barkana

备注：: 8 pages, 9 figures, replaced with version accepted by MNRAS
DOI：: 10.1093/mnras/stu1710

摘要：

第一代恒星产生的莱曼-沃纳（LW）辐射背景可以使氢分子光解，增加恒星形成所需的暗物质晕的质量。先前的研究已经确定了在恒定LW背景下有效分子冷却所需的临界质量。然而，真实背景预计将在早期迅速增加。忽视这种演化可能会低估小晕中的恒星形成，这些小晕可能在过去LW强度低得多的时候就开始冷却。背景演化是宇宙学21厘米信号再电离前预测的一个很大的不确定性来源，这可以用未来的射电望远镜观测到。为了解决这个问题，我们进行零维的一个区域的计算，遵循的密度，化学丰度，和气体的温度在中心区域的暗物质晕，包括层次的增长和不断发展的LW背景。我们从研究随红移呈指数增加的背景下的晕的物理开始。我们发现，当强度增加慢于$J_{\rm LW}(z) \propto 10^{-z/5}$，冷却在过去是一个相对较小的影响。然后，我们自洽地计算宇宙学LW背景$z=15-50$，并发现冷却在过去由于不断发展的背景有适度的影响。最后，我们将这些结果与具有不同LW历史的三维流体动力学宇宙学模拟进行了比较。虽然只模拟了少量的晕，但结果与我们的单区计算一致。

英文摘要：

The first generation of stars produces a background of Lyman-Werner (LW) radiation which can photo-dissociate molecular hydrogen, increasing the mass of dark matter halos required to host star formation. Previous studies have determined the critical mass required for efficient molecular cooling with a constant LW background. However, the true background is expected to increase rapidly at early times. Neglecting this evolution could underestimate star formation in small halos that may have started to cool in the past when the LW intensity was much lower. Background evolution is a large source of uncertainty in pre-reionization predictions of the cosmological 21cm signal, which can be observed with future radio telescopes. To address this, we perform zero-dimentional one-zone calculations that follow the density, chemical abundances, and temperature of gas in the central regions of dark matter halos, including hierarchical growth and an evolving LW background. We begin by studying the physics of halos subjected to a background that increases exponentially with redshift. We find that when the intensity increases more slowly than $J_{\rm LW}(z) \propto 10^{-z/5}$, cooling in the past is a relatively small effect. We then self-consistently compute the cosmological LW background over $z=15-50$ and find that cooling in the past due to an evolving background has a modest impact. Finally, we compare these results to three-dimensional hydrodynamical cosmological simulations with varying LW histories. While only a small number of halos were simulated, the results are consistent with our one-zone calculations.

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