SPECTRAL LINE SURVEY TOWARD THE SPIRAL ARM OF M51 IN THE 3 AND 2 mm BANDS
SPECTRAL LINE SURVEY TOWARD THE SPIRAL ARM OF M51 IN THE 3 AND 2 mm BANDS
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DOI：
10.1088/0004-637x/788/1/4
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发表时间：
2014-04
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影响因子：
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通讯作者：
Yoshimasa Watanabe;N. Sakai;K. Sorai;S. Yamamoto
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作者：
Yoshimasa Watanabe;N. Sakai;K. Sorai;S. Yamamoto
我们用射电天文学研究所30米射电望远镜对M51（NGC 5194）旋臂的两个位置进行了3和2毫米波段的谱线测量。在本次调查中，我们已经确定了13种分子物种，包括CN，CCH，N2 H+，HNCO，和CH 3OH。此外，已检测到主要物种的六种同位素。另一方面，未检测到SiO、HC 3 N、CH 3CN和氘代物质如DCN和DCO+。DCN/HCN和DCO+/HCO+的氘分馏比分别小于0.8%和1.2%。通过比较两个不同星星形成活动位置的观测结果，发现观测到的化学成分对星星形成活动的依赖性并不强。它们似乎反映了在1千秒差距尺度范围内平均的化学成分，包括许多巨大的分子云。在检测到的分子CN，CCH和CH 3OH被发现是丰富的。CN和CCH的高丰度与上述分子广泛分布的图像一致，因为它们可以通过光解离产生。另一方面，它似乎有可能是CH 3OH释放在气相中的冲击与大规模的现象，如云-云碰撞和/或非热解吸过程，如光蒸发由于宇宙射线诱导的紫外光子。目前的结果表明，一个巨大的分子云复杂的螺旋臂，它可以作为一个标准的参考研究活动星系核和星爆的化学特征的化学成分。
We have conducted a spectral line survey in the 3 and 2 mm bands toward two positions in a spiral arm of M51 (NGC 5194) with the Institut de Radioastronomie Millimétrique 30 m telescope. In this survey, we have identified 13 molecular species, including CN, CCH, N2H+, HNCO, and CH3OH. Furthermore, six isotopologues of the major species have been detected. On the other hand, SiO, HC3N, CH3CN, and deuterated species such as DCN and DCO+ were not detected. The deuterium fractionation ratios are evaluated to be less than 0.8% and 1.2% for DCN/HCN and DCO+/HCO+, respectively. By comparing the results of the two positions with different star formation activities, we have found that the observed chemical compositions do not strongly depend on star formation activities. They seem to reflect a chemical composition averaged over the 1 kpc scale region including many giant molecular clouds. Among the detected molecules CN, CCH, and CH3OH are found to be abundant. High abundances of CN and CCH are consistent with the above picture of a widespread distribution of molecules because they can be produced by photodissociation. On the other hand, it seems likely that CH3OH is liberated in the gas phase by shocks associated with large-scale phenomena such as cloud–cloud collisions and/or by nonthermal desorption processes such as photoevaporation due to cosmic-ray-induced UV photons. The present result demonstrates a characteristic chemical composition of a giant molecular cloud complex in the spiral arm, which can be used as a standard reference for studying chemistry in active galactic nuclei and starbursts.