MITEoR: a HERA pathfinder instrument for cheaper 21 cm precision cosmology

通过红移21厘米的线绘制整个宇宙中的中性氢，为探索宇宙“黑暗时代”和第一个发光物体的形成提供了一个独特的机会。此外，由于它可以映射我们宇宙的更大体积，它有可能超越宇宙微波背景，成为再电离、暴胀、暗物质、暗能量和中微子质量时代最灵敏的宇宙学探测器。这一潜力已经激发了越来越多的社区兴趣，反映在氢时代的再电离阵列（HERA）的努力和Astro 2010年十年回顾，最初的重点是技术开发和演示。这项研究的目标是开发一个数字无线电干涉仪后端与一个新的架构，测试它与64双极化天线阵列，并在110-190兆赫范围内生成覆盖大部分天空的校准前景图，所有这些都将有助于HERA的进一步发展。通过利用分层天线网格和4维快速傅立叶变换（FFT），所提出的相关器成本随着独立元件的数量而缩放为N log N，而不是像其他HERA路径查找器实验那样缩放为N^2，从而允许显著的成本节省/收集面积增加。此外，N个独立的天空光束同时成像，提高映射灵敏度。通过利用该天线网格中的大量基线冗余，可以使所有天线的增益和相位校准更加精确和完全自动化。这反过来又可以产生合成光束和初级光束的更精确的建模，这已被证明可以提高前景建模和去除的质量，这对21 cm宇宙学至关重要。拟议的MIT再电离时代（MITEoR）仪器将建立在NSF资助的开源CASPER FPGA硬件平台上，确保我们开发的技术和仪器可以被全球社区使用，并纳入未来的HERA仪器，无论其天线设计和频率范围如何。特别是，目前大规模的未来无线电阵列（如HERA-II和SKA）的愿景涉及大型紧凑的核心，我们将开发的技术可以提供最低的相关器成本和最准确的校准。沿着加强新兴的宇宙学标准模型的基础，这项研究应该开发广泛有用的技术，算法和工具。分层FFT成像思想也与其他领域相关，例如，寻找无线电瞬变和可能的微波背景极化。与过去一样，我们工作的这些产品对更广泛的社区（数据，算法，软件等）有用。将立即公开。拟议的研究还将提供有价值的学生培训。此外，由于宇宙的起源、演变和命运吸引了公众的想象力，我们的小组将继续积极参与关于这一专题的正式和非正式的公共宣传活动。

Mapping neutral hydrogen throughout our Universe via its redshifted 21 cm line offers a unique opportunity to probe the cosmic "dark ages" and the formation of the first luminous objects. Moreover, because it can map a much larger volume of our Universe, it has the potential to overtake the cosmic microwave background as the most sensitive cosmological probe of the epoch of reionization, inflation, dark matter, dark energy, and neutrino masses. This potential has stimulated growing community interest, reflected by the Hydrogen Epoch of Reionization Arrays (HERA) effort and the Astro2010 Decadal Review, with initial focus of technology development and demonstration.The goal of this research is to develop a digital radio interferometer back-end with a novel architecture, test it with a 64 dual-polarization antenna array, and generate calibrated foreground maps covering much of the sky at 110-190 MHz, all of which will help further HERA development. By exploiting a hierarchical antenna grid and 4-dimensional Fast Fourier Transforms (FFT), the proposed correlator cost scales as N log N with the number of independent elements rather than as N^2 like other HERA pathfinder experiments, allowing significant cost savings/collecting area increases down the road. Also, N independent sky beams are imaged simultaneously, improving mapping sensitivity. By exploiting the massive baseline redundancy in this antenna grid, gain and phase calibration for all antennas can be made significantly more accurate and fully automated. This can in turn produce more accurate modeling of the synthesized and primary beams, which has been shown to improve the quality of the foreground modeling and removal which is so crucial to 21 cm cosmology.The proposed MIT Epoch of Reionization (MITEoR) instrument will be built on the NSF-funded open-source CASPER FPGA hardware platform, ensuring that the technology and instrumentation that we develop can be used by the worldwide community and incorporated into future HERA instruments, regardless of their antenna design and frequency range. In particular, most current visions for massive future radio arrays (like HERA-II and SKA) involve large compact cores, for which the technology that we will develop arguably offers both the lowest correlator cost and the most accurate calibration.Along with strengthening the foundation for the emerging standard model of cosmology, this research should develop broadly useful technology, algorithms and tools. The hierarchical FFT imaging idea is also relevant to other areas, e.g., the search for radio transients and perhaps microwave background polarization.As in the past, such products of our work useful to the broader community (data, algorithms, software, etc.) will promptly be made publicly available. The proposed research will also provide valuable student training. Furthermore, since the origin, evolution and fate of the universe have captivated the imagination of the general public, our group will continue to be very engaged in both formal and informal public outreach activities on this topic.