Harvesting ALFALFA: Tracking the Gas-Rich Halos at z=0

星系最初是如何形成的，以及它们在一生中是如何变化的，这是天体物理学中最不被理解的问题之一。许多项目都集中在解开这些谜团上。该项目的目的是在宇宙学上首次对富含气体的晕进行普查，并打算提供重要的洞察，以了解一些大质量星系如何在不将气体转化为恒星的情况下维持巨大的气库，以及孤立的低质量晕如何能够保留一些原子氢气，尽管它们的热状态脆弱，势井较浅。这项提案旨在结束之前由国家科学基金会资助的已经启动的调查。可以理解的是，调查的结论主要是由于望远镜停机而推迟的，但应该会在2012年秋季完成。调查是在阿雷西博射电望远镜进行的，使用的是阿雷西博L波段馈电阵列(ALFA)，阿雷西博遗产快速阿尔法(ALFA)。这项调查已经在这一领域产生了远远超过上一次调查的结果，调查结果将有助于描述这种晕的质量函数，并使之能够与目前Lambda-CDM范例中的宇宙理论模拟进行直接比较。紫花苜蓿是一项河外HI 21厘米的测线，它将识别在高纬度天空中超过7000平方度的Z0.06范围内发现的携带HI的天体。公开的紫花苜蓿数据库包括HI线光谱和HI线位置、红移、速度宽度和通量密度的星表，以及最可能的光学对应物在其他数字数据集中的坐标和交叉识别。该项目还具有更广泛的教育影响。研究生将密切参与项目的所有阶段，帮助规划和执行观测方案，开发数据处理和分析软件，制作公共数据产品，与虚拟天文台对接，以及开展自己的科学项目。作为该项目一部分开发的教育材料将通过现有的紫花苜蓿公共网站提供。

Precisely how galaxies initially form and how they change throughout their lifetime are among the least understood problems in astrophysics. Many projects are centered on unraveling these mysteries. This project aims to provide the first robust census of gas-rich halos over a cosmologically significant volume and intends to provide important insight into how some massive galaxies maintain huge gas reservoirs without converting their gas into stars and how isolated low mass halos are able to retain some atomic hydrogen gas despite their fragile thermal state and shallow potential wells. This proposal is intended to conclude the already initiated survey, previously funded by NSF. The conclusion of the survey was understandably delayed primarily by telescope downtime but should conclude by the fall of 2012.The survey is conducted at the Arecibo radio telescope and uses the Arecibo L-band Feed Array (ALFA), the Arecibo Legacy Fast ALFA (ALFALFA). The survey has already produced results far exceeding the previous survey in this field, and the survey results will help to characterize the mass function of such halos and allow direct comparison with theoretical simulations of Universe in the current Lambda-CDM paradigm. ALFALFA, an extragalactic HI 21 cm line survey, will identify HI-bearing objects found over 7000 square degrees of the high galactic latitude sky out to z 0.06. The public ALFALFA database includes HI line spectra and catalogues of HI line positions, redshifts, velocity widths, and flux densities as well as coordinates and cross-identifications in other digital data sets of the most probable optical counterparts.This project has educational broader impacts as well. Graduate students will be intimately involved in all phases of the project, helping to plan and execute the observing program, developing software for data processing and analysis, producing public data products and interfacing with the Virtual Observatory, as well as undertaking their own science projects. Educational materials that are developed as part of this project will be made available through the existing ALFALFA public web site.