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

第一批恒星、星系和黑洞在所谓的宇宙黎明期间的形成是观测宇宙学的下一个前沿。 在这一时期，星系际介质（IGM）主要是中性氢气的形式，可以通过其红移的21厘米线进行观测。 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，将中性氢的自旋温度与IGM中的物理气体温度耦合起来。人们认为这导致了21厘米线在宇宙微波背景（CMB）的吸收中变得可见。 后来，长距离传播的X射线将其能量转化为热量，并提高了IGM的温度。这种加热驱使平均21 cm信号上升到CMB以上的发射，直到中性气体最终在再电离时期被电离，并且没有可检测的信号残留。在早期IGM中这些吸收和发射特征的演化在宇宙射电频谱中应该是明显的，因为红移映射到21厘米线的频率。必须解决重大的观测挑战，将预期的10-100 mK高红移21 cm信号与占主导地位的银河前景发射分开，但是，亚利桑那州立大学的贾德·鲍曼博士和他在马萨诸塞州理工学院的合作者提出，要克服这些挑战，就必须研制一种频谱仪，这种频谱仪的性能要提高10倍，频率覆盖范围从40 MHz到200 MHz红移范围为6 z 30。新仪器名为EDGES-2，将使用一种新的精确校准方法，该方法基于经典噪声波传播模型的推广。 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，该方法可应用于射电天文学以外的领域，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环境中的培训和指导机会，以学习数字信号处理，软件设计，统计分析，模型拟合和天体物理学的基本原理。EDGES-2项目的开发资金由NSF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.