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.
The appearance of the first stars, galaxies, and black holes is calledCosmic Dawn, and occurs when the Universe is just 100 million years old.One of the very few ways to probe this interesting time in the historyof the Universe is by looking at the 21 cm line of hydrogen. At theseearly times the hydrogen line is redshifted by the expansion of the universe to 46 MHz. This frequency range has been largely unexploredand only recently became available in the USA with the advent of the Long Wavelength Array. The first station of the LWA, called "LWA1" has been operating since2011 as a general user facility. The LWA1 has been used to look atJupiter, the Sun, meteors, pulsars, and Cosmic Dawn. The Cosmic Dawnexperiment is particularly challenging because the sky is so bright atlong wavelengths (10,000 K; see Figure), and the signal that we aresearching for is at best 0.1 K. To date we have not detected theCosmic Dawn signal, but our limits are improving. Besides supporting the LWA1 telescope to look for Cosmic Dawn, thisaward allowed many students, both undergraduate and graduate, to learnhow to operate the LWA1 and to use it for their own scientificresearch projects. We have developed a real-time all- sky imaging webpage called "LWA-TV" which shows the sky over the LWA1 in the radio.LWA-TV has grown enormously in popularity in recent months and nowroutinely sees on average 70 unique IP addresses each day, and over2000 unique IP addresses each month. For more information on the LWA see the web pages at http://lwa.unm.edu.
