Collaborative Research: Observing Cosmic Dawn with the Long Wavelength Array

在大爆炸后不久，宇宙黎明出现了，并以第一批恒星、黑洞和星系的形成为特色。中性氢气在这一时期主宰了宇宙，现在可以通过其红移的21厘米线在射电波段中探测到，最初表现为宇宙微波背景中的一条吸收线。随着第一批恒星的生命周期结束，第一批黑洞形成，附着在黑洞上的物质产生X射线，加热了星际介质(IGM)。当IGM被加热时，21厘米长的中性氢气谱线从产生的吸收线移动到发射线，直到气体在再电离时期被电离，从而消除了可检测到的信号。拟议的两年研究项目是利用新墨西哥州现有的第一个长波阵站(LWA1)采用一种新的观测策略来探测这种红移的21厘米长的线信号。LWA1由256个双极化偶极天线组成，数字组合在空中形成多个波束。虽然吸收和发射特征的时间历史在全天空射电频谱上留下了印记，但观测挑战是将大约100mK的信号与主要的银河系前景发射分开。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来消除困扰其他仪器的校准不确定性。研究人员预计，他们的努力将导致在z=25的红移处首次探测到21厘米的吸收信号，这将为早期恒星形成和IGM打开一个新的窗口。在教育方面，由于两所大学的少数族裔入学率都很高，该项目将积极寻求让未被充分代表的学生群体参与进来，该项目将资助一名研究生两年，并将在包括数字信号处理、软件设计、统计分析、模型拟合和天体物理原理在内的跨学科环境中为学生提供培训和指导的机会。

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.The proposed two-year research project is to 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.