Cosmic-ray Induced Destruction of CO in Star-forming Galaxies
Cosmic-ray Induced Destruction of CO in Star-forming Galaxies
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DOI：
10.3847/1538-4357/aa696d
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发表时间：
2017-04-20
影响因子：
4.9
通讯作者：
Zhang, Zhi-Yu
中科院分区：
文献类型：
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作者：
Bisbas, Thomas G.;van Dishoeck, Ewine F.;Zhang, Zhi-Yu
我们探索了预期较高的宇宙射线（CR）电离率zeta CR对恒星形成星系H-2云中一氧化碳（CO）、原子碳(C)和电离碳（C+）丰度的影响。Bisbas等人的研究扩展为。(a)使用真实的非均匀巨分子云（GMC）结构，(b)对cr诱导CO破坏背后的详细化学分析，以及(c)探索cr辐照分子气体的热状态。发现ζ (CR)大于或接近10倍（银河系）的星际介质中的CR显著降低了整个GMC质量中的[CO] / [H-2]丰度比。CO旋转线成像将显示比实际结构更团块的结构。对于zeta（CR）大于或接近100倍（银河），这种偏差变得严重，限制了有用性。用于恢复整个宇宙中富含h -2星系的结构和动力学特征的CO谱线，包括许多所谓的主序星系，其中大部分宇宙恒星形成发生。C+和C的丰度都随着zCR的增加而增加，当zeta（CR）接近（1 - 100）x（银河）时，C在整个H-2云中仍然是最丰富的。C+开始主导ζ (CR)大于或类似于10(3)x（银河）。gmc内部和致密区域的气体热态是不变的，zeta（CR）类似于（1 - 10）x （Galactic）的t -气体类似于10 K。对于类似于10(3)x（银河）的ζ (CR)，情况不再如此，t -气体达到了类似于30-50 K。最后，我们确定了OH是关键物质，其t气敏感丰度可以减轻CO在高温下的破坏。
We explore the effects of the expected higher cosmic ray (CR) ionization rates zeta CR on the abundances of carbon monoxide (CO), atomic carbon (C), and ionized carbon (C+) in the H-2 clouds of star-forming galaxies. The study of Bisbas et al. is expanded by. (a) using realistic inhomogeneous giant molecular cloud (GMC) structures, (b) a detailed chemical analysis behind the CR-induced destruction of CO, and (c) exploring the thermal state of CR-irradiated molecular gas. CRs permeating the interstellar medium with zeta(CR) greater than or similar to 10 x (Galactic) are found to significantly reduce the [CO] / [H-2] abundance ratios throughout the mass of a GMC. CO rotational line imaging will then show much clumpier structures than the actual ones. For zeta(CR) greater than or similar to 100 x (Galactic) this bias becomes severe, limiting the usefulness. of CO lines for recovering structural and dynamical characteristics of H-2-rich galaxies throughout the universe, including many of the so-called main-sequence galaxies where the bulk of cosmic star formation occurs. Both C+ and C abundances increase with rising zCR, with C remaining the most abundant of the two throughout H-2 clouds, when zeta(CR) similar to (1 - 100) x (Galactic). C+ starts to dominate for zeta(CR) greater than or similar to 10(3) x (Galactic). The thermal state of the gas in the inner and denser regions of GMCs is invariant with T-gas similar to 10 K for zeta(CR) similar to (1 - 10) x (Galactic). For zeta(CR) similar to 10(3) x (Galactic) this is no longer the case and T-gas similar to 30-50 K are reached. Finally, we identify OH as the key species whose T-gas-sensitive abundance could mitigate the destruction of CO at high temperatures.