The relationship between nearby galaxies and intergalactic absorbers

该项目旨在确定星系和它们周围的热气之间的关系。星系间介质(IGM)中被光致电离并被加热到10000 K量级温度的部分，其重量大约是星系内重子(即普通)物质的4倍。通过观察更远的活动星系核(AGN)在同一视线附近的光谱中的氢莱曼-阿尔法吸收线，可以在相对较近的星系中研究这种气体。首席研究员和合作者已经证明，红移小于0.017的莱曼-阿尔法吸收体中，约有一半位于中等大小或更大星系的约400千帕秒范围内。该小组将继续并扩展这项工作，分为四个部分：(1)利用哈勃空间望远镜宇宙起源光谱仪获得的AGN光谱档案，将统计数据改进10个数量级；(2)利用公共档案数据和地面望远镜的新观测，查明AGN所有观测视线附近的所有明亮星系；(3)利用已公布的数据和适当时的新数据，提高现有对星系距离、光度、分类和方向的估计的质量；以及(4)对单个吸光体的物理条件进行深入分析。目标是分别针对不同类型、大小、亮度和环境的星系，确定作为距离星系距离的函数的吸收体的性质。该项目将培训一名研究生利用天基紫外线和地面光学和无线电观测设施，其中一些涉及国际合作。该项目的一些部分将适用于本科生的研究项目，包括那些在表演机构参加正式本科生研究体验(REU)计划的学生。威斯康星大学的太空博物馆将制作一个展示星系外物质存在的展览。

This project aims to determine the relationship between galaxies and the hot gas surrounding them. The portion of the intergalactic medium (IGM) that is photo-ionized and heated to temperatures of order 10,000 K outweighs the baryonic (i.e., ordinary) matter inside galaxies by roughly a factor of 4. This gas can be studied in relatively nearby galaxies by observing the hydrogen Lyman-alpha absorption line in the spectra of more distant active galactic nuclei (AGN) near the same line of sight. The Principal Investigator and collaborators have shown that about half of the Lyman-alpha absorbers at redshifts less than 0.017 are located within about 400 kiloparsecs of a moderate-sized or larger galaxy. The team will continue and expand upon this work, in four parts: (1) improve the statistics by a factor of order 10 using archival AGN spectra obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope; (2) identify all bright galaxies near all observed AGN lines of sight, using public archival data and new observations with ground-based telescopes; (3) improve the quality of the existing estimates of galaxy distances, luminosities, classifications, and orientations, using published data and new data when appropriate; and (4) perform an in-depth analysis of the physical conditions in individual absorbers. The goal is to determine the properties of the absorbers as a function of distance from the galaxy, separately for galaxies of different types, sizes, luminosities and environments. This project will train a graduate student to make use of space-based ultraviolet and ground-based optical and radio observational facilities, some involving international collaborations. Some parts of the project will be made appropriate for research projects for undergraduate students, including those participating in the formal Research Experience for Undergraduates (REU) program at the performing institution. An exhibit illustrating the existence of matter outside galaxies will be created for the Space Place museum at the University of Wisconsin.