The Milky Way Galaxy at 21-cm

银河系平面上的大多数恒星、尘埃和气体都集中在横跨南部天空的一个只有几百平方度的窄带中。天文学家对这个区域进行了深入的研究，特别是那些研究无线电、红外线和x射线辐射的天文学家，这些辐射没有被星际介质所掩盖。这个项目由明尼苏达大学的约翰·迪基博士领导，是对银河系第一和第四象限这一区域的光谱调查，使用了21厘米的中性原子氢（HI）线。这个项目是成功的南银河平面测量（SGPS）的延伸，SGPS是由明尼苏达大学领导的美国和澳大利亚天文学家之间的合作。该调查使用了澳大利亚国家望远镜设施的两个天文台（帕克斯和紧凑型阵列），将单碟和干涉仪数据结合在一起，以获得高角度分辨率，同时保持对大尺度亮度分布的灵敏度。与之前对南银河系的调查相比，这代表了分辨率的一个数量级的提高。现在的目标是完成银河系内部的整个区域，将SGPS与北部的加拿大银河平面测量联合起来，制作一个完整的、无缝的整个银河系盘的地图集。这将结合来自几个国家天文台的数据，包括美国国家射电天文台的绿岸望远镜和甚大阵列。这些观测揭示了星际介质（ISM）原子相的天体物理学。吸收光谱和发射光谱共同指定了整个银河系中性氢的温度和丰度，作为半径和中平面以上高度的函数。银盘上有大量由氢原子组成的星际云；调查数据提供了云、片和其他ISM特征的巨大地图集。由于原子介质是如此广泛，它可以追踪到最大的结构，比如从圆盘向上延伸到光晕的超壳层和烟囱，以释放超新星注入的高温气体。ISM中的热原子阶段和冷原子阶段是银河系演化周期的关键阶段；这个调查显示了物质是如何从一代恒星到下一代恒星的这些阶段中移动的。该项目为研究生和本科生提供了教育机会。它将成为两篇或两篇以上博士论文和几篇高级荣誉论文的主题。在公众宣传方面，调查项目将成为一个视频纪录片的主题，以及许多公众讲座。这项调查的数据将免费分发给所有人。SGPS地图已经提供给世界各地的十几位天文学家，以支持他们自己的研究。21厘米的线立方体提供了在其他波长下看到的物体的背景；这次调查的地图显示了HII区域周围区域的气体密度和速度场、分子云、超新星遗迹和各种银河系现象

AST 0307603DickeyMost of the stars, dust, and gas in the plane of the Milky Way are concentrated in a narrow band of only a few hundred square degrees across the southern sky. This area is intensely studied by astronomers, particularly those working with radio, infrared, and X-ray radiation that are not obscured by the interstellar medium. This project, led by Dr. John Dickey at the University of Minnesota, is a spectroscopic survey of this area, the first and fourth quadrants of the Galaxy, using the 21-cm line of neutral atomic hydrogen (HI). This project is an extension of the successful Southern Galactic Plane Survey (SGPS), a collaboration among astronomers in the United States and Australia led by the University of Minnesota. That survey uses the two observatories of the Australia Telescope National Facility (Parkes and the Compact Array), combining the single dish and interferometer data to obtain high angular resolution while preserving the sensitivity to the largescale brightness distribution. This represents an order of magnitude improvement in resolution over previous surveys of the Southern Milky Way. Now the goal is to complete the entire area of the inner Galaxy, to join the SGPS with the Canadian Galactic Plane Survey in the north, to produce a single, seamless atlas of the entire Milky Way disk. This will be a combination of data from observatories in several countries, including the U.S. National Radio Astronomy Observatory's Green Bank Telescope and Very Large Array. The astrophysics of the atomic phases of the interstellar medium (ISM) is revealed by these observations. Absorption and emission spectra together specify the temperature and abundance of the neutral hydrogen all over the Galaxy, as a function of radius and height above the mid-plane. Interstellar clouds of atomic hydrogen are abundant in the Galactic disk; the survey data provide a huge atlas of clouds, sheets, and other ISM features. Because the atomic medium is so widespread,it traces the largest structures, such as supershells and chimneys that reach from the disk up into the halo to vent hot gas injected by supernovae. The warm and cool atomic phases in the ISM are critical stages in the cycle of Galactic evolution; this survey shows how matter moves through these stages from one generation of stars to the next. This project provides educational opportunities for graduate and undergraduate students. It will be the subject for two or more Ph.D. theses, and several senior honors theses. In the area of public outreach, the survey project will be the subject of a video documentary, as well as many public talks. The data from this survey will be distributed freely to all. The SGPS maps have already been given to more than a dozen astronomers all over the world to support their own research. The 21-cm line cubes provide the context for objects seen at other wavelengths; maps from this survey show the gas density and velocity fields in the area surrounding HII regions, molecular clouds, supernova remnants, and all kinds of Galactic phenomena.***