Determination of Direction, Frequency and Polarization of Radio Emission from Galactic OH
Determination of Direction, Frequency and Polarization of Radio Emission from Galactic OH
复制标题
确定银河 OH 射电发射的方向、频率和偏振
作者：
A. Cook
研究氢氧根星系射电辐射的一个主要问题是，如何理解这些辐射似乎局限于非常小的明亮区域，每个区域都有一个特定的频率特征。此外，已经发现，发射可以显示线性和圆极化2,3。如果存在氢氧根分子的速度在较大距离上相关的区域，那么在特定频率上发射的局域化可以很容易地用受激发射假说来解释。如果速度沿着视线变化很大，那么相对于某些局部标准的多普勒频移也会发生，并且不会发生受激发射，因为任何特定频率的光学深度都是不够的。为了获得足够的光学深度，沿着视线的速度必须在大约1019厘米的距离上相关。在没有任何其他原因引起的波长变化的情况下，在这样一段距离内，速度沿着视线必须是恒定的。只有在有这种系统运动的方向上，才能观察到强烈的发射。观测到的光谱中峰的频率表明，一个源的不同部分的速度可能相差100 km/s（参考文献1）。
A MAJOR problem in the study of galactic radio emission from OH is to understand how it is that the emissions appear to be localized in very small bright regions each characterized by a particular frequency1; in addition, it has been found that emissions can show both linear and circular polarization2,3. The localization of emission at a particular frequency can readily be explained on the hypothesis of stimulated emission4 if there are regions in which the velocities of the OH molecules are correlated over large distances. Should the velocities vary considerably along a line of sight, so will the Doppler shifts relative to some local standard and stimulated emission will not occur because the optical depth at any particular frequency would be inadequate. For a sufficient optical depth, the velocities along the line of sight must be correlated over a distance of about 1019 cm. In the absence of shifts of wave-length from any other cause, the velocity must be constant along the line of sight over such a distance. Only in those directions along which there is such a systematic motion will intense emission be observed. The frequencies of peaks in observed spectra indicate that velocities in different parts of a source may differ by 100 km/s (ref. 1).