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藏——几乎完全由原子氢（HI）和分子氢（H2）组成——转化为恒星。天文学家已经对这一过程形成了令人印象深刻的详细图景，包括“氢循环”，原子和分子气体通过这种循环从一种形式转变为另一种形式，然后再转变回来。阿塔卡马大型毫米波阵列（ALMA）彻底改变了对极遥远（z 3）星系中H2的研究，它利用了像一氧化碳（CO）这样的高光“示踪”分子。为了探测星系的HI含量，天文学家必须依靠更弱的21厘米HI“自旋翻转”跃迁，这有效地限制了对局部（z 0.2）宇宙的研究。该项目的目标是将星系中的HI普查扩展到前所未有的红移z = 1.45，并通过使用MeerKAT阵列（LADUMA）调查来观察遥远的宇宙，填补我们目前对HI在星系演化中的作用的理解的关键空白。该项目由PI联合领导，已经与南非的64单元MeerKAT射电望远镜一起获得了3424小时的高优先级时间，以对扩展钱德拉深空南部的单个超深点进行成像。支持观测将用于允许HI“叠加”观测，以及区分HI和OH超激光发射。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）前体科学方面继续保持领导地位。该奖项还将支持一名尖端科学研究生的培训，以及一项针对新泽西州社区学院的新拓展计划。结果将来自直接的HI光谱线探测，以及通过“堆叠”先前测量位置和红移的星系样本。后者将允许LADUMA充分发挥其潜力，研究HI到z = 1.45，至少在统计意义上。该项目还包括在HI样本中识别OH超级激光“闯入者”，该样本将用于追踪z = 1.86的富含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Astro2020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（“揭示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？)，以及优先用于星系演化研究的关键发现区域（“绘制星系周围介质和星系间介质的发射图”）。该奖项反映了美国国家科学基金会的法定使命，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.