H2 Formation in Low-Metallicity Galaxies
H2 Formation in Low-Metallicity Galaxies
复制标题
低金属丰度星系中 H2 的形成
DOI：
10.1093/pasj/53.3.483
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发表时间：
2001
期刊：
影响因子：
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通讯作者：
H. Hirashita
中科院分区：
文献类型：
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作者：
H. Kamaya;H. Hirashita
研究了银河系尺度上氢分子的一种可能形成机制。我们特别感兴趣的是氢分子在原始星系形成和演化中的作用。因此，在一个非常低的金属丰度星系（I Zw 18;最典型的缺金属星系）的氢分子的形成过程进行了研究。采用最近对I Zw 18中氢分子吸收线的观测结果，我们获得了氢分子可以通过H −过程形成的情况下电离度的上限，尽管它们通常被认为是在尘埃颗粒表面形成的。此外，我们提出了一个临界电离度，在该电离度以上，H −过程可以在晶粒表面的形成过程中占主导地位。有趣的是，该临界电离度与I Zw 18的电离度上限相当。为了确定氢分子的形成过程，未来的观测设施可能是有用的。因此，我们研究了在某些波长的金属缺乏星系的可探测性。根据我们的估计，氢分子的近红外线发射可以在10 μJy的水平上观察到，自由-自由射电发射在mJy的水平上，而氢分子形成的尘埃的远红外发射也可以在10-mJy的水平上检测到，其温度为16 K。近红外线和远红外连续谱线对于ASTRO-F观测是可行的。
A possible formation mechanism of hydrogen molecules on a galactic scale is examined. We are interested especially in the role of hydrogen molecules for the formation and evolution of primordial galaxies. Thus, the formation process of hydrogen molecules in a very low-metallicity galaxy (I Zw 18; the most typical metal-deficient galaxy) is studied. Adopting a recent observational result of the absorption lines of hydrogen molecules in I Zw 18, we obtain the upper limit for the ionization degree in the case where hydrogen molecules can form via the H − -process, although they are generally believed to form on the surface of dust grains. Furthermore, we present a critical ionization degree, above which the H − -process can be dominant over the formation process on the surface of grains. Interestingly, this critical ionization degree is comparable to the upper limit of the ionization degree for I Zw 18. For determining the formation process of hydrogen molecules, future observational facilities can be useful. Thus, we examine the detectability in some wavelengths for metal-deficient galaxies. According to our estimate, the nearinfrared line emission of hydrogen molecules is observable at the level of 10 µJy, the free–free radio emission is at the level of mJy, and the far-infrared emission from the dust on which hydrogen molecules form can also be detected at the 10-mJy level with its temperature of 16K. The near-infrared line and the far-infrared continuum are feasible for ASTRO-F observations.