Collaborative Research: Observing Cosmic Dawn with the Long Wavelength Array

宇宙大爆炸后不久，宇宙黎明出现了，并形成了第一批恒星，黑洞和星系。 中性氢气在这个时期主导了宇宙，现在可以通过其红移的21厘米线在无线电波段中检测到，最初表现为宇宙微波背景中的吸收线。 随着第一批恒星的生命周期结束和第一批黑洞的形成，吸积到黑洞上的物质产生了X射线，加热了星系际介质（IGM）。 当IGM被加热时，中性氢气的21厘米线从产生吸收线移动到发射线，直到气体在再电离时期被电离，从而消除了可检测的信号。这项为期两年的研究计划将采用一种新的观测策略，利用新墨西哥州现有的第一个长波阵列站（LWA 1）来检测这种红移的21厘米线信号，它由256个双极化偶极天线组成，这些天线被数字组合以在天空中形成多个波束。 虽然吸收和发射特征的时间历史被印在全天空无线电频谱上，但观测的挑战是将大约100 mK的信号与占主导地位的银河前景发射分开。 研究人员的策略利用独特的波束形成能力，通过同时瞄准科学和校准器领域，消除困扰其他仪器的校准不确定性。 研究人员希望他们的努力能够导致在z=25的红移处首次检测到21厘米的吸收信号，这将为早期星星形成和IGM打开一个新的窗口。在教育方面，由于这两个机构都有很高的少数民族入学率，这个项目将积极寻求参与代表性不足的学生群体，它将资助一名研究生两年，并将为学生提供跨学科环境中的培训和指导机会，包括数字信号处理，软件设计，统计分析，模型拟合，和天体物理学

A short time after the Big Bang, the Cosmic Dawn emerged and featured the formation of the first stars, black holes, and galaxies. Neutral hydrogen gas dominated the Universe during this epoch and is now detectable in the radio bands through its redshifted 21-cm line, initially manifest as an absorption line in the cosmic microwave background. As the life cycle of the first stars ended and the first black holes formed, matter accreting onto the black holes produced X-rays, which heated the intergalactic medium (IGM). As the IGM was heated, the 21-cm line of the neutral hydrogen gas moved from producing absorption lines to emission lines until the gas was ionized during the epoch of reionization, thus removing the detectable signal.This two-year research project will employ a novel observing strategy to detect this redshifted 21-cm line signal using the existing first Long Wavelength Array station (LWA1) in New Mexico, which consists of 256 dual-polarization dipole antennas that are digitally combined to form multiple beams on the sky. While the time history of the absorption and emission features is imprinted on the all-sky radio spectrum, the observational challenge is to separate the approximately 100 mK signal from the dominant Galactic foreground emission. The investigators' strategy exploits the unique beam forming capability to remove calibration uncertainties that plague other instruments by simultaneously targeting science and calibrator fields. The investigators expect to their efforts to lead to the first detection of the 21-cm absorption signal at a redshift of z=25 that will open a new window on early star formation and the IGM.Educationally, as both institutions have high minority enrollment, this project will actively seek to involve underrepresented student groups, and it will fund a graduate student for two years and will provide opportunities for student training and mentoring in an interdisciplinary environment including principles of digital signal processing, software design, statistical analysis, model fitting, and astrophysics.