高速云研究进展

High-Velocity Clouds

1963年通过氢21 cm谱线观测发现了高速云(HVCs),40多年来其起源一直是天文界争论的焦点之一。近几年通过高分辨率观测、理论模型和数值模拟,对其中几类高速云及全天性的研究有了很大突破。主要介绍一些研究进展,包括对新发现的两类致密高速云和高度电离高速云的总体性及个别性的观测研究;对南天区最大的MS和北天区最大的Complex C的高分辨率观测;唯一确定了Complex A的距离在4-10 kpc之间;利用Hα发射线对高速云的距离作了粗略的限制;而在高速云内寻找恒星的努力都以失败告终。另外还简单介绍了一些试图解释高速云起源的理论模型和数值模拟。

High-velocity clouds (HVCs) were first detected by HI 21 cm emission in 1963, since then the nature of HVCs remains controversial although more than forty years has been pasted. In the last decade, with the observations of high resolutions, the developments of theoretical models and numerical simulations, there has been great progress in many aspects of the studies of high-velocity clouds, particularly for some special kinds and the all-sky surveys. In this paper, main progress is reviewed including the observational studies of the two kinds of newly-found CHVCs and highly-ionized HVCs as a whole or individually, the high-resolution observations of Magellanic Stream and Complex C which are the largest HVCs in Southern and Northern sky respectively, as well as the one and only convincing constraint on the distance of Complex A which is in the range of 4-10 kpc from the Galactic center. Some theoretical models and simulations trying to explain the origins of HVCs are introduced briefly. This paper will also give brief descriptions on how to constrain the galactic distances of HVCs using Ha emission lines and the so far failed efforts to find stars in HVCs.