PROBING THE PHYSICAL CONDITIONS OF ATOMIC GAS AT HIGH REDSHIFT
PROBING THE PHYSICAL CONDITIONS OF ATOMIC GAS AT HIGH REDSHIFT
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DOI：
10.1088/0004-637x/800/1/7
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发表时间：
2014-11
期刊：
影响因子：
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通讯作者：
M. Neeleman;J. Prochaska;A. Wolfe
中科院分区：
文献类型：
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作者：
M. Neeleman;J. Prochaska;A. Wolfe
本文提出了一种测量阻尼Lyα系统中气体物理状态的新方法。使用高分辨率的吸收光谱的样品的80个DLAs，我们能够测量的比率的上，下精细结构的基态的C+和Si+。这些比率完全由气体的物理条件决定。我们探索允许的物理参数空间，使用蒙特卡罗马尔可夫链方法同时约束的温度，中性氢密度，和电子密度的每个DLA。结果表明，至少有5%的DLAs的大部分气体处于致密的冷态，典型密度为100 cm−3，温度低于500 K。我们进一步发现，在我们的样本中，DLAs的典型压强为log（P/kB）= 3.4（K cm−3），这与本地星际介质（ISM）的压强相当，并且包含大量中性气体的组分可以非常小，吸收尺寸可以小到几个秒差距。我们表明，大多数系统的密度明显高于纯正则暖中性介质的预期密度，这表明大量的致密气体（即，nH > 0.1 cm−3）来匹配观测值。最后，我们确定了8个系统的Si II* 的阳性检测。这些系统的压强（P/kB）超过20，000 K cm−3，这表明这些系统在年轻的恒星形成星系中具有高度湍流的ISM。
A new method is used to measure the physical conditions of the gas in damped Lyα systems (DLAs). Using high-resolution absorption spectra of a sample of 80 DLAs, we are able to measure the ratio of the upper and lower fine-structure levels of the ground state of C+ and Si+. These ratios are determined solely by the physical conditions of the gas. We explore the allowed physical parameter space using a Monte Carlo Markov chain method to constrain simultaneously the temperature, neutral hydrogen density, and electron density of each DLA. The results indicate that at least 5% of all DLAs have the bulk of their gas in a dense, cold phase with typical densities of ∼100 cm−3 and temperatures below 500 K. We further find that the typical pressure of DLAs in our sample is log (P/kB) = 3.4 (K cm−3), which is comparable to the pressure of the local interstellar medium (ISM), and that the components containing the bulk of the neutral gas can be quite small with absorption sizes as small as a few parsecs. We show that the majority of the systems are consistent with having densities significantly higher than expected for a purely canonical warm neutral medium, indicating that significant quantities of dense gas (i.e., nH > 0.1 cm−3) are required to match observations. Finally, we identify eight systems with positive detections of Si ii*. These systems have pressures (P/kB) in excess of 20,000 K cm−3, which suggest that these systems tag a highly turbulent ISM in young, star-forming galaxies.