Molecular Hydrogen in Infrared Cirrus
Molecular Hydrogen in Infrared Cirrus
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红外卷云中的分子氢
DOI：
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发表时间：
2005
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通讯作者：
J. Shull
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作者：
K. Gillmon;K. Gillmon;J. Shull
我们将最近对 50 个高纬 AGN 的星际分子氢吸收的 FUSE 调查数据与 COBE 校正的 IRAS 100 μm 发射图结合起来，研究红外卷云与 H2 的相关性。 H2 柱密度与 IR 卷云强度的关系图显示分子分数 f 的转变与总氢柱密度 NH 相同。这种转变通常归因于 H2“自屏蔽”，它表明许多弥漫卷云中含有大量 H2，f ≈ 1%-30%。这些云在 b > 30°、温度校正 100 μm 强度 D ≥ 1.5 MJy sr-1 时覆盖了约 50% 的北方天空。片状卷云的氢密度nH≥30 cm-3，可能被盘-晕界面处的动力学过程压缩，有利于颗粒表面氢气的形成。利用 N 和 100 μm 强度之间的相关性，我们估计 b > 30° 的卷云在 H2 中包含约 3000 M☉。外推到银河系内部，卷云可能含有 107 M☉ 的 H2 和 108 M☉ 的气体总质量。如果提高到 100 pc，它们的重力势能约为 1053 尔格。
We combine data from our recent FUSE survey of interstellar molecular hydrogen absorption toward 50 high-latitude AGNs with COBE-corrected IRAS 100 μm emission maps to study the correlation of infrared cirrus with H2. A plot of the H2 column density versus IR cirrus intensity shows the same transition in molecular fraction, f, as seen with total hydrogen column density, NH. This transition is usually attributed to H2 "self-shielding," and it suggests that many diffuse cirrus clouds contain H2 in significant fractions, f ≈ 1%-30%. These clouds cover ~50% of the northern sky at b > 30°, at temperature-corrected 100 μm intensities D ≥ 1.5 MJy sr-1. The sheetlike cirrus clouds, with hydrogen densities nH ≥ 30 cm-3, may be compressed by dynamical processes at the disk-halo interface, and they are conducive to H2 formation on grain surfaces. Exploiting the correlation between N and 100 μm intensity, we estimate that cirrus clouds at b > 30° contain ~3000 M☉ in H2. Extrapolated over the inner Milky Way, the cirrus may contain 107 M☉ of H2 and 108 M☉ in total gas mass. If elevated to 100 pc, their gravitational potential energy is ~1053 ergs.