Twenty-one Centimeter Hydrogen Line Studies of Galaxy Evolution

附近的星系有着异常大量的中性 氢气可以用射电天文学来研究 技术. 观察的目的是确定 大型富含气体的星系的气体结构， 现在有一些动态过程在起作用， 过去很重要。 一个合作计划，使用新的接收系统， 韦斯特博克（荷兰）综合射电望远镜 （WSRT）将开始研究高度红移的21厘米 氢气的波长吸收线。 仪器 非常适合这种实验 光学勘测 已经在进行的星系研究将提供 研究无线电波长的候选人。 重要的是要 强调射电天文学技术补充了 光学数据，提供：（1）甚长基线 空间范围的VLBI干涉测量 吸收气体，（2）中性氢气（HI）温度 估计，以及（3）高列中的运动学细节 密度云在吸收系统的中心。 这 该计划将是一个合作的努力与天文学家从 匹兹堡大学和天文学家。 VLBI谱线实验将开展竞争 在WSRT。 PKS 0458-02中的星系系统（红移z = 2.04）非常适合更详细的研究。 有收音机 背景源中的结构在广泛的尺度上，以及 吸收本身是非常强的。 的精度 该系统的谱线VLBI观测将得到改善 并将尝试中等长度的基线实验， 其应检测典型吸收器上的结构 银河尺度 包括WSRT在内的四站VLBI实验， 阿雷西博、绿色银行和乔德雷尔银行将非常有用，因为 WSRT-Jodrell Bank基线将足够短， 大前吸收（约2弧秒） 结构 洲际基线将检测到 结构中的吸收器对更紧凑的组件。 阿雷西博和绿色银行都已经配备了接收器。 Jodrell Bank正在计划建造一座低噪音的建筑。 为了在实验中包括250英尺的望远镜。 由于接收系统已改进了约4倍， 由于进行了先前的实验， 用VLBI方法观测了1999年以来的低红移系统（z = 0.69）， 将重复3C 286的光谱。 包括WSRT和 Jodrell Bank在这个实验中会引起极大的兴趣，因为 3C 286中的背景射电源（如PKS 0458-020）具有 在广泛的规模上。 该项目的成果 应该提高我们对结构和演变的理解 银河系。

Nearby galaxies which have an unusually large amount of neutral hydrogen gas can be studied by radio astronomical techniques. The objectives of the observations will be to define the gaseous structures of large, gas-rich galaxies and to see if there are dynamical processes at work now that might have been important in the past. A collaborative program that uses the new receiving systems at the Westerbork (The Netherlands) Synthesis Radio Telescope (WSRT) will be initiated to study the highly redshifted 21 cm wavelength absorption line of hydrogen gas. The instrument is uniquely suited to this type of experiment. The optical survey work on the galaxies which is already in progress will provide candidates for study at radio wavelengths. It is important to emphasize that radio astronomy techniques complement the optical data by providing: (1) Very Long Baseline Interferometric (VLBI) measurements of the spatial extent of the absorbing gas, (2) the neutral hydrogen gas (HI) temperature estimates, and (3) details of the kinematics in the high column density clouds at the heart of the absorption system. This program will be a collaborative effort with an astronomer from the University of Pittsburgh and Netherland astronomers. VLBI spectral line experiments will be carried out to compete with the WSRT. The galaxy system in PKS 0458-02 (redshift z = 2.04) is well-suited to more detailed study. There is radio structure in the background source on a wide range of scales, and the absorption itself is very strong. The precision of the spectral line VLBI observations of this system will be improved and intermediate-length baseline experiments will be attempted, which should detect the structure in the absorber on typical galactic scales. A four-station VLBI experiment including WSRT, Arecibo, Green Bank, and Jodrell Bank would be very useful since the WSRT-Jodrell Bank baseline would be short enough to define the absorption in front of the large (about 2 arcsecond) structure. The intercontinental baselines would detect the fine structure in the absorber against the more compact components. Both Arecibo and Green Bank are already equipped with receivers. Jodrell Bank is planning to build a low noise preamplifier in order to include the 250-foot telescope in the experiment. Since receiving systems have improved by a factor of about 4 in sensitivity since the previous experiment was performed, the VLBI observations of the lower redshift systems (z = 0.69) in the spectrum of 3C286 will be repeated. The inclusion of WSRT and Jodrell Bank in this experiment would be of great interest since the background radio source in 3C286, like PKS 0458-020, has structure on a wide range of scales. The results of the project should improve our understanding of the structure and evolution of galaxies.