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“再电离时期”。 这是宇宙大爆炸后数亿年的一个时期，在此期间，宇宙中所有的原子氢气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。 这是因为宇宙的性质（以及导致电离的物体）对星系如何形成的模型和模拟以及被电离物质的物理学（星系际介质或IGM）具有影响。 该项目将通过对再电离期后的IGM进行观测，为再电离和高红移星系提供新的认识。 在这些时候，IGM包含了大量关于再电离何时以及如何发生的信息。幸运的是，在过去的一年里，人们发现了一组“超亮”类星体，它们比以前已知的类似距离的类星体要亮得多。PI和他的团队将对再电离后IGM的三个方面进行全新或大大改进的测量：（i）由于再电离过程中的加热，IGM中重子的平滑，（ii）由于再电离后冷却，IGM的热变化，以及（iii）迄今为止最敏感的研究，从这个时期开始，在星系中富集比氦重的元素。 后一种测量方法将有助于理解早期星星的形成。该项目支持的教育工作将覆盖以西班牙裔为主的低收入社区的幼儿。由该补助金资助的PI和研究生将帮助开发，管理和执行天文学主题的研讨会，旨在促进幼儿园，一年级和二年级学生的STEM教育。研讨会将讨论加州的共同核心国家标准的科学，并针对服务不足的社区在滨江和周边地区。工作坊的主题将包括触摸宇宙，螺旋宇宙，无处不在的星座和宇宙的气味。这个项目显然与NSF的使命，以促进科学的进步。 此外，该项目的“更广泛的影响”部分也是这样做的，通过帮助培养下一代不同个体对STEM活动的兴趣和教育，促进国民健康，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。沿着宇宙最后一次全球相变，再电离对星系形成模型和星系际介质（IGM）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、宇宙微波背景辐射和其他探测器的观测，已经取得了显著的进展。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。受这些新对象的激励，PI和他的团队将对再电离后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平滑将揭示有多少能量在较高的红移处通过光加热注入，因此当发生再电离时（更多的总加热=更早的再电离）。这种测量将把再电离的特征红移限制在Δ zreion =+/-0.7以内，或者比目前的CMB限制好两倍。(ii)测量IGM的温度到有史以来最高的红移（z=5.7）将确定IGM在那个时期是否仍然温暖，因为最近被重新电离。或者，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的CIV测量将对金属敏感到宇宙平均密度，探测的体积比任何红移的任何其他直接测量多六倍。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。寻找z~6处的弱O I系统也将确定在z 5处C IV随红移的下降是否是由于金属丰度的下降或UV背景的演变。

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.