Nobeyama 45 m Cygnus-X CO巡天I：无偏大尺度CN和C $^{18}$ O图揭示的分子光解离
Nobeyama 45m Cygnus-X CO survey I: photodissociation of molecules revealed by the unbiased large-scale CN and C$^{18}$O maps
摘要：
我们提出了一个无偏的大规模（9度$^2$）CN（$N$ =1-0）和C $^{18}$ O（$J$ =1-0）的天鹅座-X的调查与Nobeyama 45米天鹅座-X CO调查。CN和C $^{18}$ O在朝向天鹅座-X南北的各种物体中被检测到（例如，DR 17、DR 18、DR 21、DR 22、DR 23和W75 N）。我们发现CN/C $^{18}$ O的积分强度比在不同的区域有系统的差异，特别是在被附近OB星照射的DR 17和DR 18中得到增强。这一结果表明，CN/C $^{18}$ O比率通过光解离反应得到提高。研究了CN/C $^{18}$ O比值与紫外辐射场强度的关系。结果发现，CN/C $^{18}$ O比值与远紫外强度$G_0$相关。我们还发现，CN/C $^{18}$ O的比例下降的分子云内，星际紫外辐射减少，由于星际尘埃消光。结果表明，CN/C $^{18}$ O比值受紫外辐射的控制，是一个很好的探测光子主导区域的探针。
英文摘要：
We present an unbiased large-scale (9 deg$^2$) CN ($N$=1-0) and C$^{18}$O ($J$=1-0) survey of Cygnus-X conducted with the Nobeyama 45m Cygnus-X CO survey. CN and C$^{18}$O are detected in various objects towards the Cygnus-X North and South (e.g., DR17, DR18, DR21, DR22, DR23, and W75N). We find that CN/C$^{18}$O integrated intensity ratios are systematically different from region to region, and are especially enhanced in DR17 and DR18 which are irradiated by the nearby OB stars. This result suggests that CN/C$^{18}$O ratios are enhanced via photodissociation reactions. We investigate the relation between the CN/C$^{18}$O ratio and strength of the UV radiation field. As a result, we find that CN/C$^{18}$O ratios correlate with the far-UV intensities, $G_0$. We also find that CN/C$^{18}$O ratios decrease inside molecular clouds, where the interstellar UV radiation is reduced due to the interstellar dust extinction. We conclude that the CN/C$^{18}$O ratio is controlled by the UV radiation, and is a good probe of photon-dominated regions.
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