Probing the Conditions for the H i-to-H2 Transition in the Interstellar Medium
Probing the Conditions for the H i-to-H2 Transition in the Interstellar Medium
复制标题
探索星际介质中 H i 到 H2 跃迁的条件
DOI：
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发表时间：
2023
影响因子：
4.9
通讯作者：
S. Stanimirović
中科院分区：
文献类型：
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作者：
Gyueun Park;Min;S. Bialy;B. Burkhart;J. Dawson;C. Heiles;Di Li;C. Murray;Hiep Nguyen;Anita Hafner;D. Rybarczyk;S. Stanimirović
我们通过分析 58 个银河视线 (LOS) 的 Hi 发射和吸收测量值以及 12CO(1–0) (CO) 和尘埃数据，研究了太阳附近 H i 到 H2 转变的条件。基于冷中性介质和温中性介质（CNM 和 WNM）的精确柱密度，我们首先将气体分解为原子相和分子相，并表明观察到的 LOS 大多以 H i 为主。此外，我们发现CO-暗H2，而不是光学厚的H i，是太阳附近暗气体的主要成分。为了研究 CO 亮分子气体的形成条件，我们分析了 H i 和 CO 之间的运动学关联，发现 CNM 在运动学上比 WNM 与 CO 的关联更密切。当 CO 线宽内的 CNM 分量被隔离时，我们发现以下特征：自旋温度 < 200 K，峰值光学深度 > 0.1，CNM 分数 ~0.6，以及 V 波段尘埃消光 > 0.5 mag。这些结果表明，CO 亮分子气体优先在高柱密度的环境中形成，其中 CNM 变得更冷且更丰富。最后，我们将观察到的 CNM 特性与 Sternberg 等人的稳态 H2 形成模型进行比较。并推断 CNM 一定是块状且体积填充系数较小。另一种可能性是模型中缺失的过程，例如宇宙射线和气体动力学，在 H i 到 H2 的转变中发挥着重要作用。
We investigate the conditions for the H i-to-H2 transition in the solar neighborhood by analyzing H i emission and absorption measurements toward 58 Galactic lines of sight (LOSs) along with 12CO(1–0) (CO) and dust data. Based on the accurate column densities of the cold and warm neutral medium (CNM and WNM), we first perform a decomposition of gas into atomic and molecular phases, and show that the observed LOSs are mostly H i-dominated. In addition, we find that the CO-dark H2, not the optically thick H i, is a major ingredient of the dark gas in the solar neighborhood. To examine the conditions for the formation of CO-bright molecular gas, we analyze the kinematic association between H i and CO, and find that the CNM is kinematically more closely associated with CO than the WNM. When CNM components within CO line widths are isolated, we find the following characteristics: spin temperature < 200 K, peak optical depth > 0.1, CNM fraction of ∼0.6, and V-band dust extinction > 0.5 mag. These results suggest that CO-bright molecular gas preferentially forms in environments with high column densities where the CNM becomes colder and more abundant. Finally, we confront the observed CNM properties with the steady-state H2 formation model of Sternberg et al. and infer that the CNM must be clumpy with a small volume filling factor. Another possibility would be that missing processes in the model, such as cosmic-rays and gas dynamics, play an important role in the H i-to-H2 transition.
DOI：
10.3847/2041-8213/ac1f95
发表时间：
2021-09
期刊：
The Astrophysical Journal Letters
影响因子：
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作者：
S. Bialy;C. Zucker;A. Goodman;M. Foley;J. Alves;V. Semenov;R. Benjamin;R. Leike;T. Enßlin
通讯作者：
S. Bialy;C. Zucker;A. Goodman;M. Foley;J. Alves;V. Semenov;R. Benjamin;R. Leike;T. Enßlin