LADUMA: Reaching the Highest Redshifts with the Deepest HI Survey

自从它们在早期宇宙中形成以来，星系一直在将它们的气体库-几乎完全由原子（HI）和分子氢（H2）组成-转化为恒星。天文学家已经形成了一个令人印象深刻的详细的图像，包括“氢循环”，其中原子和分子气体从一种形式转变到另一种形式，然后再回来。阿塔卡马大型毫米波阵列（阿尔马）利用一氧化碳（CO）等高度发光的“示踪”分子，彻底改变了对极远（z 3）星系中H2的研究。为了探测星系的HI含量，天文学家必须依赖于HI的21 cm“自旋翻转”跃迁，这有效地限制了对本地（z 0.2）宇宙的研究。该项目的目标是将星系中的HI普查扩展到z = 1.45的前所未有的红移，并通过用MeerKAT阵列（LADUMA）调查来填补我们目前对HI在星系演化中的作用的理解中的关键空白。该项目由PI联合领导，已获得南非64单元MeerKAT射电望远镜的3，424小时高优先级时间，以在扩展的Chandra Deep Field South中成像单个超深指向。将使用辅助观测来进行HI“叠加”观测以及区分HI和OH超脉泽发射。所有调查数据将公开发布。该项目将使美国在平方公里阵列（SKA）前兆科学方面继续保持领导地位。该奖项还将支持尖端科学研究生的培训，以及新泽西社区大学的新推广计划。结果将来自两个直接HI谱线检测和“堆叠”样品的星系与以前测量的位置和红移。后者将允许LADUMA实现其研究HI到z = 1.45的全部潜力，至少在统计意义上是这样。该项目还包括在HI样本中识别OH超脉泽“闯入者”，这将用于追踪z = 1.86的富气体合并的宇宙历史。这些研究活动将受益于与理论模型的详细比较，并与最近发布的2020年天文学和天体物理学十年调查的“宇宙生态系统”主题非常匹配，包括该主题的优先科学领域（“揭开星系增长的隐藏驱动因素”），一个科学问题（“气体，金属和尘埃如何流入和流出星系？”），该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Since their formation in the early universe, galaxies have been converting their gas reservoirs - almost entirely composed of atomic (HI) and molecular hydrogen (H2) - into stars. Astronomers have formed an impressively detailed picture of this process, including the "hydrogen cycle" by which atomic and molecular gas transition from one form to the other and back again. The study of H2 in extremely distant (z 3) galaxies has been revolutionized by the Atacama Large Millimeter Array (ALMA), which takes advantage of highly luminous "tracer" molecules like carbon monoxide (CO). To probe the HI content of galaxies astronomers must rely on the much weaker 21 cm "spin-flip" transition of HI, which has effectively restricted studies to the local (z 0.2) universe. This project's goal is to extend this HI census in galaxies to the unprecedented redshift of z = 1.45 and fill a crucial gap in our current understanding of HI’s role in galaxy evolution through the Looking At the Distant Universe with the MeerKAT Array (LADUMA) survey. The project, jointly led by the PI, has been awarded 3,424-hours of high-priority time with the 64-element MeerKAT radio telescope in South Africa to image a single ultra-deep pointing in the Extended Chandra Deep Field South. Supporting observations will be used to allow HI "stacking" observations as well as discriminating HI from OH megamaser emission. All survey data will be publicly released. This project will allow continued U.S. leadership in Square Kilometer Array (SKA) precursor science. The award will also support the training of a graduate student in cutting-edge science as well as a new outreach program to community colleges in New Jersey. Results will be derived from both direct HI spectral line detections and by “stacking” samples of galaxies with previously measured positions and redshifts. The latter will allow LADUMA to achieve its full potential for studying HI out to z = 1.45, at least in a statistical sense. The project also encompasses the identification of OH megamaser “interlopers” in the HI sample that will be used to trace the cosmic history of gas-rich mergers out to z = 1.86. These research activities will benefit from detailed comparisons to theoretical models and are well-matched to the “cosmic ecosystems” theme of the recently released Astro2020 Decadal Survey on Astronomy and Astrophysics, including that theme’s priority science area (“unveiling the hidden drivers of galaxy growth”), a science question (“How do gas, metals, and dust flow into and out of galaxies?”), as well as a critical discovery area prioritized for galaxy evolution research (“mapping the circumgalactic medium and the intergalactic medium in emission”).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.