Collaborative Research: Large-Aperture Experiment to Detect the Dark Age (LEDA)

技术摘要探测黑暗时代的大孔径实验（LEDA）项目旨在探测宇宙大爆炸（红移16-40）后约1亿年的星系际介质中中性氢（21厘米静止波长）的超精细发射。探测将为结构形成模型以及宇宙中第一批恒星和黑洞的形成提供第一个观测约束。LEDA将开发信号处理仪器并将其集成到长波长阵列（LWA）的新的第一站中。这包括一个大N相关器，为LWA-1的所有512个偶极天线提供服务，利用分组CASPER架构，并将FPGA和GPU结合起来用于F和X级。迭代校准和成像将依赖于扭曲快照成像，并从GPU支持的库（CUWARP）中提取，该库专门设计用于支持固定偶极阵列的宽场全极化成像。校准技术将包括对电离层折射和方向相关偶极增益的校正，以及探索脉冲星数据分析以提高性能。精确的校准和成像将是LEDA的关键要求，需要减去明亮的前景天空和检测微弱的中性氢信号。从计算的角度来看，LEDA是一个O（100）万亿次每秒的挑战，使一个可扩展的架构，期待发展的无线电阵列，要求功率高效的10千万亿次每秒的性能。氢时代再电离阵列（HERA 2）的第二阶段就是一个例子。这些恒星的质量要比我们现在周围的恒星大得多。超大质量黑洞是同时形成的，还是更早，还是更晚？今天宇宙学的最大挑战之一就是对这些第一代天体的研究。它们的形成被广泛假设在大爆炸后大约1亿年开始，但没有数据可以验证这一理论。研究如此年轻的宇宙（只有今天的1%）的唯一可用手段是通过恒星和黑洞之间的星系际介质的电磁辐射。今天，这是热的和电离的等离子体，但在早期宇宙中，它是一个巨大的冷中性氢气库，为第一批恒星和黑洞的形成提供了食物，并辐射出大量的长波长辐射。LEDA项目旨在应用前沿射电天文学技术来首次探测这种信号。LEDA将建造一个“无线电照相机”，用于部署到长波长阵列，这是一个位于新墨西哥州的射电望远镜，其第一个100米直径的孔径最近完成。LEDA相机将结合联合收割机多种创新技术和数据分析技术，为学生和年轻科学家提供参与尖端科学和开发最先进工具的机会。特别是，LEDA将利用图形处理单元（GPU）的巨大计算能力和灵活性-为视频游戏提供动力的引擎-以10米波长制作几乎整个天空的瞬时图像（比可见光辐射长1000万倍）。从这些图像中，我们和其他星系的光线将被高精度地减去，从而能够搜寻宇宙诞生之初的信号LEDA将推动宇宙学的前沿，同时为未来的射电天文学设施奠定基础，大规模计算和信号处理系统将成为关键。LEDA努力的跨学科成果将有利于天文学、计算和太阳科学。

Technical AbstractThe Large Aperture Experiment to Detect the Dark Ages (LEDA) project seeks to detect hyperfine emission from neutral Hydrogen (21 cm rest wavelength) in the intergalactic medium about 100 million years after the Big Bang (redshifts 16-40). A detection would deliver the first observational constraints on models of structure formation and on the formation of the first stars and black holes in the Universe. LEDA will develop and integrate signal processing instrumentation into the new first station of the Long Wavelength Array (LWA). This comprises a large-N correlator serving all 512 dipole antennas of the LWA-1, leveraging a packetized CASPER architecture and combining FPGAs and GPUs for the F and X stages. Iterative calibration and imaging will rely on warped snapshot imaging and be drawn from a GPU-enabled library (CUWARP) that is designed specifically to support wide-field full polarization imaging with fixed dipole arrays. Calibration techniques will include correction for ionospheric refraction and direction dependent dipole gains, and exploration of pulsar data analysis to improve performance. Accurate calibration and imaging will be crucial requirements for LEDA, necessary to subtract the bright foreground sky and detect the faint neutral Hydrogen signal. From the computational standpoint, LEDA is a O(100) TeraFlop per second challenge that enables a scalable architecture looking toward development of radio arrays requiring power efficient 10 PetaFlop per second performance. Stage two of the Hydrogen Epoch of Reionization Array (HERA2) is one example.Lay AbstractWhen did the first stars form? These stars are expected to be much more massive than the stars that are around us today. Did supermassive black holes form at the same time, earlier, or later? One of the great challenges of cosmology today is the study of these first generation objects. Their formation is widely hypothesized to have begun about 100 million years after the Big Bang, but no data are available to test this theory. The only available means to study the Universe at so young an age (just 1% of what it is today) is via electromagnetic radiation from the intergalactic medium between the stars and black holes. Today, this is hot and ionized plasma, but in the early Universe it was a vast reservoir of cold neutral Hydrogen gas that fed the formation of the first stars and black holes and radiated long wavelength radiation copiously.The LEDA project seeks to apply frontier radio astronomical techniques to make the first detection of this signal. LEDA will build a "radio camera" for deployment to the Long Wavelength Array, a radio telescope in New Mexico whose first 100m-diameter aperture was recently completed. The LEDA camera will combine several innovative technologies and data analysis techniques, giving students and young scientists the opportunity to join in cutting-edge science and development of the most advanced tools. In particular, LEDA will harness the massive computing power and flexibility of Graphics Processing Units (GPUs) - the engines that power video games - to make instantaneous images of nearly the whole sky at up to 10 meters wavelength (10 million times longer than visible radiation).From these images the light of our and other galaxies will be subtracted with high accuracy, enabling a search for signals from the dawn of the Universe. LEDA will push the frontiers of cosmology while contributing groundwork for future radio astronomical facilities where massive computing and signal processing systems will be lynchpins. Cross-disciplinary outgrowths of the LEDA effort will benefit astronomical, computational and solar sciences.