Probing the Epoch of Reionization with the Brightest High-Redshift Quasars

宇宙早期历史中的一个重要时期是所谓的“再电离时代”。这是宇宙大爆炸后几亿年的一段时间，在这段时间里，宇宙中所有的氢原子都被新形成的大质量恒星电离。它们是宇宙中最早形成的恒星。了解这个早期阶段是天体物理学的主要目标之一。这是因为宇宙（以及引起电离的物体）的特性对星系如何形成以及被电离物质（星系间介质或IGM）的物理特性的模型和模拟具有影响。该项目将通过观测再电离时代之后的IGM，为再电离和高红移星系提供新的线索。在这些时候，IGM包含了大量关于再电离发生的时间和方式的信息。幸运的是，在过去的一年里，一组“超亮”类星体被发现，它们比以前已知的距离相似的类星体要亮得多。PI和他的团队将对再电离后的IGM的三个方面进行全新或大大改进的测量：(i)再电离期间加热导致的IGM中重子的平滑，（ii）再电离后冷却导致的IGM的热变化，以及（iii）迄今为止最敏感的研究，即从这一时期开始，星系中比氦更重的元素的富集。后一种测量将有助于理解早期恒星的形成。该项目支持的教育工作将惠及以西班牙裔为主的低收入社区的幼儿。这项资助的PI和研究生将帮助开发、管理和举办以天文学为主题的研讨会，旨在促进幼儿园、一年级和二年级学生的STEM教育。这些研讨会将讨论加州的共同核心州科学标准，并针对河滨及周边地区服务不足的社区。研讨会主题将包括触摸宇宙，螺旋宇宙，星座无处不在，以及宇宙的气味。这个项目显然与美国国家科学基金会促进科学进步的使命有关。此外，该项目的“更广泛的影响”部分做到了这一点，并通过帮助培养对下一代不同个人的STEM活动的兴趣和教育来促进国家的健康、繁荣和福利。了解再电离时代仍然是天体物理学的前沿目标之一。再电离作为宇宙最后的全局相变，对星系形成模型和星系间介质（IGM）的物理学具有重要意义。在过去的几年里，通过对高红移星系、类星体、宇宙微波背景和其他探测器的观测，取得了显著的进展。然而，目前关于再电离何时发生的综合约束仍然相对较弱，大部分观测结果与再电离结束相对较晚（z~6-7）或明显较早（z~8-9）相一致。在这些新天体的激励下，PI和他的团队将对再电离后的IGM和星系-IGM界面的三个方面进行全新或大大改进的测量：(i)测量z~5处IGM的Jeans平滑将揭示通过光加热在更高红移处注入了多少能量，从而揭示再电离发生的时间（更多的总加热=更早的再电离）。这一测量将把再电离的特征红移限制在Deltazreion=+/-0.7以内，或者比目前的CMB约束好两倍。（ii）测量IGM的温度直到最高的红移（z=5.7）将确定IGM在最近被再电离的那个时代是否仍然是温暖的。另外，一个已经冷却到z~5.5的IGM将意味着再电离主要发生在z7.5。（iii）最后，在z~5处对CIV进行的调查将对金属敏感到宇宙平均密度，探测的体积比任何其他在任何红移处的直接调查多六倍。这将首次揭示再电离时代的星系通过星系风丰富其周围环境的全部程度。在z~6寻找弱O - I系统也将确定在z5红移的C - IV的下降是由于金属丰度的下降还是由于UV背景的演化。

An important period in the early history of the universe is the so-called "epoch of reionization". This is a period a few hundred million years after the Big Bang during which all of the atomic Hydrogen gas in the universe was ionized by newly formed massive stars. These were the first stars to form in the universe. Understanding this early period is one of the main goals of astrophysics. This is because properties of the unverse (and the objects causing the ionization) carry implications for models and simulations of how galaxies form and the physics of the matter being ionized (the intergalactic medium or IGM). This project will shed new light on reionization and high-redshift galaxies by observing the IGM after the epoch of reionization. At these times, the IGM contains a large amount of information on when and how reionization occurred. Fortunately, in the past year a set of "ultra-bright" quasars have been discovered that are much brighter than previously known quasars at similar distances. The PI and his team will make entirely new or greatly improved measurements of three aspects of the post-reionization IGM: (i) the smoothing of baryons in the IGM due to heating during reionization, (ii) the thermal changes of the IGM due to cool-down following reionization, and (iii) the most sensitive study to date of the enrichment of elements heavier than helium of gas in galaxies from this period. This latter measurement will aid in the understanding of early-period star formation.Education efforts supported by this project will reach young children in predominantly Hispanic, low-income communities. The PI and graduate student funded by this grant will help to develop, manage, and perform astronomy-themed workshops designed to promote STEM education in kindergarten, first, and second-grade students. The workshops will address California's Common Core State Standards for science, and target underserved communities in Riverside and surrounding areas. Workshop themes will include Touching the Universe, The Spiral Universe, Constellations Everywhere, and Smells of the Universe. This project clearly relates to NSF's mission to promote the progress of science. In addition, the "Broader Impact" portion of the project does this, and advances the national health, prosperity and welfare by helping to develop interest in, and educating, STEM activities among the next generation of diverse individuals.Understanding the epoch of reionization remains one of the forefront goals of astrophysics. Along with being the last global phase change of the Universe, reionization carries key implications for models of galaxy formation and the physics of the intergalactic medium (IGM). Over the past several years, notable advances have been made through observations of high-redshift galaxies, quasars, the cosmic microwave background, and other probes. Currently, however, the combined constraints on when reionization occurred remain relatively weak, with the bulk of observations being consistent with reionization ending either relatively late (z~6-7) or significantly earlier (z~8-9).Motivated by these new objects, the PI and his team will make entirely new or greatly improved measurements of three aspects of the post-reionization IGM and galaxy-IGM interface: (i) Measuring the Jeans smoothing of the IGM at z~5 will reveal how much energy has been injected at higher redshifts via photo-heating, and hence when reionization occurred (more total heating = earlier reionization). This measurement will constrain the characteristic redshift of reionization to within Deltazreion=+/-0.7, or a factor of two better than current CMB constraints. (ii) Measuring the temperature of the IGM out to the highest redshifts ever (z=5.7) will determine whether the IGM is still warm at that epoch from having recently been reionized. Alternatively, an IGM that has already cooled by z~5.5 will imply that reionization largely occurred at z7.5. (iii) Finally, the survey for CIV at z~5 will be sensitive to metals down to the cosmic mean density, probing a factor of six more volume than any other direct survey at any redshift. This will reveal, for the first time, the full extent to which reionization-era galaxies enriched their surroundings via galactic winds. Searching for weak O I systems at z~6 also will establish whether the drop in C IV with redshift at z5 is due to a decline in metallicity or evolution of the UV background.