We report on one of the highest sensitivity surveys for molecular lines in the frequency range 6.0 to 7.4 GHz conducted to date. The observations were done with the 305m Arecibo Telescope toward a sample of twelve intermediate/high-mass star forming regions. We searched for a large number of transitions of different molecules, including CH3OH and OH. The low RMS noise of our data (~5 mJy for most sources and transitions) allowed detection of spectral features that have not been seen in previous lower sensitivity observations of the sources, such as detection of excited OH and 6.7 GHz CH3OH absorption. A review of 6.7 GHz CH3OH detections indicates an association between absorption and radio continuum sources in high-mass star forming regions, although selection biases in targeted projects and low sensitivity of blind surveys imply incompleteness. Absorption of excited OH transitions was also detected toward three sources. In particular, we confirm a broad 6.035 GHz OH absorption feature in G34.26+0.15 characterized by an asymmetric blue-shifted wing indicative of expansion, perhaps a large scale outflow in this HII region.

中文翻译：

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使用阿雷西博望远镜对分子线进行高灵敏度观测

我们报告了迄今为止对 6.0 至 7.4 GHz 频率范围内的分子谱线进行的最高灵敏度调查之一。观测是使用 305m 阿雷西博望远镜对十二个中/高质量恒星形成区域的样本进行的。我们搜索了大量不同分子的跃迁，包括 CH3OH 和 OH。我们数据的低 RMS 噪声（对于大多数源和跃迁约为 5 mJy）允许检测在以前对源的低灵敏度观察中没有看到的光谱特征，例如检测激发的 OH 和 6.7 GHz CH3OH 吸收。对 6.7 GHz CH3OH 探测的回顾表明，在大质量恒星形成区域中吸收和射电连续源之间存在关联，尽管目标项目的选择偏差和盲目调查的低灵敏度意味着不完整。还检测到对三个来源的激发 OH 跃迁的吸收。特别是，我们确认了 G34.26+0.15 中广泛的 6.035 GHz OH 吸收特征，其特征是不对称的蓝移机翼表明膨胀，可能是该 HII 区域的大规模外流。