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首页> 外文期刊>The Astrophysical journal >EVIDENCE FOR THE LARGE-SCALE DISSOCIATION OF MOLECULAR GAS IN THE INNER SPIRAL ARMS OF M81
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EVIDENCE FOR THE LARGE-SCALE DISSOCIATION OF MOLECULAR GAS IN THE INNER SPIRAL ARMS OF M81

机译：M81内旋臂中分子气体大规模分离的证据

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摘要

We compare the detailed distributions of H Ⅰ, Hα, and 150 nm far-UV (FUV) continuum emission in the spiral arms of M81 at a resolution of 9″ (linear resolution 150 pc at 3.7 Mpc distance). The bright Hα emission peaks are always associated with peaks in the FUV emission. The converse is not always true; there are many regions of FUV emission with little corresponding Hα. The H Ⅰ and the FUV are always closely associated, in the sense that the H Ⅰ is often brightest around the edges of the FUV emission. The effects of extinction on the morphology are small, even in the FUV. Extensive FUV emission, often with little corresponding Hα, indicates the presence of many "B stars," which produce mostly nonionizing UV photons. These FUV photons dissociate a small fraction of an extensive layer of H_2 into H Ⅰ. The observed morphology can be understood if "chimneys" are common in the spiral arms of M81, where holes are blown out of the galactic disk, exposing the bright H Ⅱ regions and the corresponding FUV associated with vigorous star formation. These "naked" star-forming regions show little obscuration. H_2 is turned into H Ⅰ by UV photons impinging on the interior surfaces of these chimneys. The intensity of the FUV radiation measured by the Ultraviolet Imaging Telescope can dissociate the underlying H_2 with a typical density of ～10 H nuclei cm~(-3) to produce the observed amount of H Ⅰ in the spiral arms of M81. Except for thin surface layers locally heated in these photodissociation regions that are close to the FUV sources, the bulk of the molecular gas in the inner disk of M81 is apparently too cold to produce much ~(12)CO(1-0) emission.
机译：我们比较了M81旋臂中HⅠ，Hα和150 nm远紫外（FUV）连续发射的详细分布，其分辨率为9英寸（在3.7 Mpc距离处的线性分辨率为150 pc）。明亮的Hα发射峰始终与FUV发射峰相关。相反，并非总是如此。 FUV发射区域很多，相应的Hα很少。 HⅠ和FUV始终紧密相关，因为HⅠ通常在FUV发射的边缘周围最亮。消光对形态的影响很小，即使在FUV中也是如此。广泛的FUV发射（通常对应的Hα很少）表明存在许多“ B星”，这些B星主要产生非电离的UV光子。这些FUV光子将一小部分H_2分解为HⅠ。如果“烟囱”在M81的旋臂中很常见，则可以理解观察到的形态，在烟囱中，从银河盘上吹出了洞，露出了明亮的HⅡ区和与剧烈的恒星形成有关的FUV。这些“裸露”的恒星形成区域几乎没有遮盖。紫外线光子撞击这些烟囱的内表面，使H_2变成HⅠ。用紫外线成像望远镜测量的FUV辐射强度可以使下方的H_2分解，其典型密度约为10 H核cm〜（-3），从而在M81的旋臂中产生观察到的HⅠ量。除了在靠近FUV源的这些光解离区域中局部加热的薄表面层外，M81内盘中的大部分分子气体显然太冷，无法产生大量〜（12）CO（1-0）发射。

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