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

Arizona State University, Scottsdale AZ

Investigators

Abstract

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.