LADUMA: Reaching the Highest Redshifts with the Deepest HI Survey

自早期宇宙形成以来，星系一直在将其气库--几乎完全由原子(HI)和分子氢(H2)组成--转变为恒星。天文学家已经对这一过程形成了一幅令人印象深刻的详细图景，其中包括原子和分子气体从一种形式转化为另一种形式并再次转化的“氢循环”。阿塔卡马大型毫米波阵列(ALMA)利用一氧化碳(CO)等高亮度“示踪”分子，彻底改变了对极远(Z3)星系中H2的研究。要探测星系的HI含量，天文学家必须依靠HI弱得多的21厘米“自旋-翻转”转变，这实际上限制了对局部(z0.2)宇宙的研究。这个项目的目标是将星系的HI普查扩展到前所未有的z=1.45红移，并通过使用猫鼬阵列(Laduma)观测遥远的宇宙来填补我们目前对HI在星系演化中作用的理解的一个关键空白。该项目由PI联合领导，已获得南非元素猫鼬射电望远镜3424小时的高优先级时间，以成像延伸的钱德拉深场南部的单个超深指向。支持观测将被用来允许HI“叠加”观测，以及区分HI和OH超强激光发射。所有调查数据都将公开发布。该项目将使美国在平方公里阵列(SKA)前兆科学领域继续保持领先地位。该奖项还将支持对一名尖端科学研究生的培训，以及新泽西州社区大学的一项新的外联计划。结果将来自于直接的HI谱线探测和将星系样本与先前测量的位置和红移“堆叠”在一起。后者将使拉杜马充分发挥其研究HI的潜力到z=1.45，至少在统计意义上是这样。该项目还包括在HI样本中识别出OH超级激光“入侵者”，这将被用来追溯丰富的气体合并的宇宙历史，直到z=1.86。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年天体天文学和天体物理学十年期调查的“宇宙生态系统”主题很好地匹配，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、金属和尘埃如何进出星系？”)，这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.