Twenty-one Centimeter Hydrogen Line Studies of Galaxy Evolution

附近有大量中性氢气的星系可以用射电天文技术进行研究。观测的目标将是确定大型、富含气体的星系的气体结构，并看看现在是否存在过去可能很重要的动力学过程。将启动一个合作项目，利用韦斯特博克(荷兰)合成射电望远镜(WSRT)的新接收系统来研究高度红移的氢气21厘米波长吸收线。这台仪器特别适合这种类型的实验。对星系的光学测量工作已经在进行中，这将为射电波长的研究提供候选。必须强调的是，射电天文学技术通过以下方式补充光学数据：(1)甚长基线干涉测量(VLBI)吸收气体的空间范围，(2)中性氢气(HI)温度估计，以及(3)位于吸收系统核心的高柱状密度云中的运动学细节。该项目将与匹兹堡大学的天文学家和荷兰天文学家共同努力。将进行VLBI谱线实验，以与WSRT竞争。PKS0458-02(红移z=2.04)中的星系非常适合于更详细的研究。背景源在大范围尺度上存在射电结构，吸收本身很强。该系统的谱线VLBI观测的精度将得到提高，并将尝试中等长度的基线实验，这将在典型的银河系尺度上探测吸收体中的结构。一个包括WSRT、阿雷西博、Green Bank和Jodrell Bank的四站VLBI实验将非常有用，因为WSRT-Jodrell Bank基线将足够短，以定义大型(约2角秒)结构前面的吸收。洲际基线将相对于更紧凑的组件来检测吸收体中的精细结构。阿雷西博和绿色银行都已经配备了接收器。Jodrell Bank正计划建造一台低噪声前置放大器，以便将这台250英尺长的望远镜纳入实验。由于自上一次实验以来，接收系统的灵敏度提高了约4倍，因此将重复3C286光谱中较低红移系统(z=0.69)的VLBI观测。将WSRT和Jodrell Bank包括在这个实验中将是非常有意义的，因为3C286中的背景射电源与PKS 0458-020一样，具有广泛的尺度结构。该项目的结果应该会提高我们对星系结构和演化的理解。

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.