Collaborative Research: Finding the Gas that Lights up Galaxies

阻尼莱曼- α (DLA)系统，具有中性氢柱密度的低电离气体层，是现代富含气体的星系的特征，经常在背景类星体的光谱中被探测到。DLA系统是研究星系形成和宇宙中重元素富集历史的重要探测器。提案团队计划在该项目中继续他们正在进行的DLA系统工作，该项目有三个主要组成部分：(1)在红移接近5时对DLA进行调查。该团队将测量离子柱密度，以跟踪这些第一批星系中金属的积累和中性气体的演变，并将寻找接近再电离时代的电离水平的下降。(2)利用ALMA天文台在红移接近2的星系中寻找单电离碳的158微米辐射。已知目标星系具有[CII]吸收；ALMA的观测将把在发射和吸收中探测到的气体的特性联系起来，以限制它们的大小、动力学和恒星形成速率。数值模拟也将用于预测高红移星系的[CII]发射特性。(3)从DLAs成像远紫外（FUV）光。该团队将使用在哈勃超深视场中发现的红移在1到5之间的莱曼断裂星系的堆叠图像来寻找低表面亮度的发射。他们还计划利用DLA与更高红移、光学厚度吸收器的机会对准，以获得FUV中恒星形成区域的成像和光谱，并估计星系的恒星形成速率、大小和形态。该项目将支持两名研究生的工作和培训，合作的首席研究员将参加各种场合的外联讲座，包括一所特许少数民族高中和一个面向中学女生的科学节。他们维护着一个公共网站，专门针对普通公众和研究界的国防科学。该团队打算在第一次观测后的两年内通过网站发布该计划获得的所有高分辨率光谱。

Damped Lyman-alpha (DLA) systems, layers of low-ionization gas with neutral hydrogen column densities characteristic of modern, gas-rich galaxies, are frequently detected in spectra of background quasars. DLA systems are important probes of the history of galaxy formation and heavy-element enrichment in the universe. The proposing team plans to continue their ongoing work on DLA systems in this project, which has three major components: (1) A survey for DLAs at redshifts near 5. The team will measure ionic column densities, in order to track the build-up of metals in these first galaxies and the evolution of the neutral gas, and will search for a decrease in ionization level close to the re-ionization epoch. (2) A search for 158-micron emission from singly-ionized carbon in galaxies at redshifts near 2, using the ALMA observatory. The targeted galaxies are already known to have [CII] absorption; ALMA observations will connect properties of the gas detected in emission and in absorption to constrain their sizes, dynamics, and star formation rates. Numerical simulations will also be used to predict the [CII] emission properties of galaxies at higher redshift. (3) Imaging far ultraviolet (FUV) light from DLAs. The team will use stacked images of Lyman-break galaxies at redshifts between 1 and 5 identified in the Hubble ultra-deep field to search for low surface-brightness emission. They plan also to exploit the chance alignment of a DLA with a higher redshift, optically-thick absorber to obtain imaging and spectroscopy of the star-forming regions in the FUV and estimate the star formation rate, size and morphology of the galaxy. The project will support the work and training of two graduate students, and the collaborating Principal Investigators will participate in outreach talks in various venues, including a charter minority-serving high school and a science festival for middle school girls. They maintain a public website dedicated to DLA science targeted to both the general public and the research community. The team intends to release all of the high-resolution spectra obtained in this program through the website within 2 years of the first observations.