New Measurements Of The EDGES 21cm Profile

Tuesday February 5, 2019 4:00 pm

After stars form in the early Universe, their ultraviolet light alters the excitation state of the 21cm hyperfine line of neutral hydrogen gas in the intergalactic medium. This initially causes the gas to absorb photons from the cosmic microwave background. Later, energy deposited into the gas by the ultraviolet and X-ray emission from these early stars and their remnants heats the gas and eventually ionizes it. In early 2018, we reported the first evidence for detection of this redshifted 21cm signal in all-sky radio observations acquired by our Experiment to Detect the Global EoR Signature (EDGES). We found a flattened absorption profile in the sky-averaged radio spectrum centered at a frequency of 78 MHz with full width at half maximum of 19 MHz and an amplitude of 0.5 K. The frequency (redshift) of the profile is roughly consistent with astrophysical models of early star formation. However, the amplitude of the observed profile is more than a factor of two greater than the largest standard predictions and suggests that the gas was either significantly colder than expected or the background radiation temperature was hotter than expected. A number of possible explanations have been proposed, including interactions between baryons and various candidate dark matter particles, as well as possible astronomical sources capable of producing an intense radio synchrotron background in the early Universe. At the same time, although we reported a number of verification tests with the detection, concerns have been expressed that the instrument or parameter estimation procedure we used could be erroneously creating the signal. New measurements with EDGES using a scaled antenna that shifted frequency-dependent beam properties reproduced the reported profile, reducing the likelihood that instrumental artifacts are responsible for the feature. I will review the original detection, present the new measurements and additional analysis, and describe plans for a third-generation EDGES instrument that could yield improvements in the calibration accuracy and reduce frequency-dependent structure in the antenna beam pattern.


Event Contact

Debbie Meinbresse