EDGES-2: Detecting First Light and Reionization through the Global 21 cm Signature

第一批恒星、星系和黑洞的形成被称为宇宙黎明，是观测宇宙学的下一个前沿。在这一时期，星系间介质（IGM）主要以中性氢气的形式存在，通过其21厘米的红移线可以观测到。一旦第一批恒星在红移z ~ 30处形成，它们就会产生莱曼α光子的背景，将中性氢自旋温度与IGM中的物理气体温度结合起来。这被认为是导致21厘米线在宇宙微波背景（CMB）的吸收中变得可见的原因。后来，x射线长距离传播，将能量以热的形式沉积下来，提高了IGM的温度。这种加热驱使平均21厘米的信号上升到CMB上方的发射，直到中性气体最终在再电离时期被电离，没有可检测到的信号留下。这些吸收和发射特征在IGM早期的演变应该在宇宙无线电频谱中很明显，因为红移映射到21厘米线的频率。要将预期的10-100 mK高红移21厘米信号与主要的银河系前景发射分离开来，必须解决重大的观测挑战，但亚利桑那州立大学的贾德·鲍曼博士和他在麻省理工学院的合作者建议用一种性能提高10倍的光谱仪来克服这些挑战，这种光谱仪的频率覆盖范围从40到200 MHz，可以跨越红移范围6 z 30。这台名为EDGES-2的新仪器将采用一种基于经典噪声波传播模型的新精密校准方法。该项目的更广泛影响包括演示这种新的宽带系统高精度校准方法，该方法在射电天文学之外也有应用，包括电离层研究。该项目还非常注重为本科生和研究生提供跨学科培训和指导的机会，让他们学习数字信号处理、软件设计、统计分析、模型拟合和天体物理学的基本原理。edge -2项目的开发资金由美国国家科学基金会天文科学部通过其先进技术和仪器计划提供。

The formation of the first stars, galaxies, and black holes during what is known as the Cosmic Dawn is the next frontier in observational cosmology. During this epoch, the intergalactic medium (IGM) was primarily in the form of neutral hydrogen gas, accessible to observations through its redshifted 21 cm line. Once the first stars formed at a redshift z ~ 30, they produced a background of Lyman-alpha photons that coupled the neutral hydrogen spin temperature to the physical gas temperature in the IGM. This is thought to have caused the 21 cm line to become visible in absorption against the cosmic microwave background (CMB). Later, X-rays traveling long distances deposited their energy as heat and raised the IGM temperature. This heating drove the average 21 cm signal to rise into emission above the CMB, until the neutral gas was eventually ionized during the epoch of reionization, and no detectable signal remained. The evolution of these absorption and emission features in the early IGM should be evident in cosmic radio spectrum, since redshift maps to frequency for the 21 cm line. Significant observational challenges must be addressed to separate the expected 10-100 mK high-redshift 21 cm signal from the dominant Galactic foreground emission, but Dr. Judd Bowman of the Arizona State University and his collaborators at the Massachusetts Institute of Technology propose to overcome these challenges with a spectrometer featuring 10 times improved performance and frequency coverage from 40 to 200 MHz to span the redshift range 6 z 30. The new instrument, called EDGES-2, will make use of a new precision calibration method based on a generalization of the classic noise wave propagation model. Broader impacts of the project include demonstration of this new, high-precision calibration method for wideband systems, which has applications outside of radio astronomy, including to ionospheric study. The project also has a strong focus on providing opportunities for undergraduate and graduate student training and mentoring in an interdisciplinary environment to learn basic principles of digital signal processing, software design, statistical analysis, model fitting, and astrophysics. Funding for the development of the EDGES-2 project is being provided by NSF's Division of Astronomical Sciences through its Advanced Technologies and Instrumentation program.