Anomalously Excited OH and Competition between Maser Transitions toward Centaurus A
Anomalously Excited OH and Competition between Maser Transitions toward Centaurus A
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异常兴奋的 OH 和微波激射器向半人马座 A 过渡的竞争
DOI：
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发表时间：
1995
期刊：
影响因子：
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通讯作者：
F. Israel
中科院分区：
文献类型：
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作者：
H. V. van Langevelde;E. V. van Dishoeck;M. Sevenster;F. Israel
利用澳大利亚望远镜紧凑阵观测到了OH向邻近活动星系半人马座A核的基态射电跃迁。在静止频率1667和1665 MHz处的主线显示分子吸收的速度与在毫米波长处观察到的其他分子物种的速度相似，这表明在无线电和毫米波长处的视线对相同的材料进行采样。在1612和1720 MHz的卫星跃迁表现出受激发射和吸收，包括第一次在1720 MHz谱线上探测到河外脉泽发射。这两个卫星跃迁的一个显著特征是它们对所有速度分量都是共轭的，一个在发射中，另一个在吸收中同样强。这被解释为在红外线刚刚变得光学厚的状态下，两条线对相同的反转红外辐射的竞争。从1720 MHz到1612 MHz脉泽发射的转变严重依赖于OH柱密度，因此可以获得有关分子气体分布的直接信息。
The ground-state radio transitions of OH have been observed toward the nucleus of the nearby active galaxy Centaurus A, using the Australia Telescope Compact Array. The main lines at rest frequencies 1667 and 1665 MHz show molecular absorption at velocities similar to those observed for other molecular species at millimeter wavelengths, which indicates that the lines of sight at radio and millimeter wavelengths sample the same material. The satellite transitions at 1612 and 1720 MHz exhibit stimulated emission and absorption, including the first extragalactic detection of maser emission in the 1720 MHz line. A remarkable feature of the two satellite transitions is that they are conjugate for all velocity components, with one in emission and the other equally strong in absorption. This is explained as the competition of the two lines for the same inverting infrared radiation in the regime in which the infrared lines are just becoming optically thick. The transition from 1720 MHz to 1612 MHz maser emission depends critically on the OH column density and therefore yields direct information on the distribution of molecular gas.