The Milky Way Galaxy at 21-cm

在银河系的平面上，大多数恒星、尘埃和气体都集中在南部天空仅几百平方度的狭窄区域内。天文学家对这一区域进行了深入的研究，特别是那些研究无线电、红外和X射线辐射的科学家，这些辐射不会被星际介质遮挡住。该项目由明尼苏达大学的约翰·迪基博士领导，利用21厘米长的中性原子氢(HI)线对这一区域进行光谱测量，该区域是银河系的第一和第四象限。这个项目是成功的南银河系平面调查(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。这项调查使用了澳大利亚望远镜国家设施的两个观测站(帕克斯和紧凑型阵列)，将单盘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敏感性。这代表着分辨率比之前对南银河系的调查提高了一个数量级。现在的目标是完成内银河系的整个区域，在北部加入SGPS和加拿大银河系平面调查，制作出整个银河系圆盘的单一、无缝的地图集。这将是来自多个国家天文台的数据组合，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一起确定了整个银河系中性氢的温度和丰度，作为中面以上半径和高度的函数。星际氢原子云在银盘中非常丰富；勘测数据提供了一个巨大的云层、薄片和其他ISM特征的地图集。由于原子介质如此广泛，它可以追踪到最大的结构，例如从盘面延伸到光晕的超壳层和烟囱，以释放超新星注入的热气体。ISM中的热原子相和冷原子相是银河系演化周期中的关键阶段；这项调查显示了物质如何从一代恒星到下一代恒星通过这些阶段。该项目为研究生和本科生提供教育机会。它将成为两篇或更多博士论文和几篇高级荣誉论文的主题。在公众宣传方面，调查项目将成为一部视频纪录片以及许多公开演讲的主题。这次调查的数据将免费分发给所有人。SGPS地图已经分发给了世界各地的十几名天文学家，以支持他们自己的研究。21厘米的线状立方体提供了在其他波长上看到的物体的背景；这份调查的地图显示了HII区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.***