Discovery of molecular hydrogen in a high-velocity cloud of the Galactic halo
Discovery of molecular hydrogen in a high-velocity cloud of the Galactic halo
复制标题
在银河晕高速云中发现分子氢
作者：
P. Richter;K. S. Boer;H. Widmann;N. Kappelmann;W. Gringel;M. Grewing;J. Barnstedt
银河系的晕包含了中性氢云，具有很高的径向速度，不遵循银河系的一般旋转运动。我们对这些高速云的距离知之甚少，因此即使是总质量这样的总体性质也很难确定。因此，关于它们的起源没有普遍接受的理论。一种观点认为，它们是由超新星推动的喷泉般的气流从银河系中喷出后冷却的气体造成的;另一种观点认为，它们是由缺乏重元素的气体组成的，这些气体从星系际空间落到银河系的盘上。分子氢的存在，其形成通常需要尘埃（因此是富含重元素的气体）的存在，可以帮助区分这些可能性。在这里，我们报告的发现分子氢吸收在高速云沿着的视线到大麦哲伦云。我们还推导出同一云的铁丰度是太阳值的一半。从这些数据中，我们得出结论，在这个云的气体起源于银河系的磁盘。
The Milky Way's halo contains clouds of neutral hydrogen with high radial velocities which do not follow the general rotational motion of the Galaxy. Few distances to these high-velocity clouds are known, so even gross properties such as total mass are hard to determine. As a consequence, there is no generally accepted theory regarding their origin. One idea is that they result from gas that has cooled after being ejected from the Galaxy through fountain-like flows powered by supernovae; another is that they are composed of gas, poor in heavy elements, which is falling onto the disk of the Milky Way from intergalactic space. The presence of molecular hydrogen, whose formation generally requires the presence of dust (and therefore gas, enriched in heavy elements), could help to distinguish between these possibilities. Here we report the discovery of molecular hydrogen absorption in a high-velocity cloud along the line of sight to the Large Magellanic Cloud. We also derive for the same cloud an iron abundance which is half of the solar value. From these data, we conclude that gas in this cloud originated in the disk of the Milky Way.