Special Seminar - "An Absorption Feature in the Sky-Averaged Radio Spectrum"

Raul Monsalve (McGill University)

Title: An Absorption Feature in the Sky-Averaged Radio Spectrum

Abstract:I will present the measurement of an absorption feature in the sky-averaged, or global, radio spectrum centered at 78 MHz by the EDGES Low-Band experiment. The measured feature is broadly consistent with the absorption of photons from the microwave back ground by neutral hydrogen gas in the intergalactic medium (IGM) due to significant star formation about 180 million years after the Big Bang. Despite this consistency, the amplitude, shape, and frequency of the feature are in tension with physical predictions for either the temperature of the IGM or the microwave background at those redshifts. In my talk I will describe the EDGES Low-Band measurement, which spans the frequency range 50-100 MHz, carried out from the desert of Western Australia, and some of the proposed physical implications if the signal is verified to be of cosmological origin. I will also describe recent instrumental tests that we have conducted, which provide further support to the cosmological/astrophysical interpretation of the absorption signal. Finally, I will present our analyses to constrain standard 21-cm models using EDGES High-Band data spanning 90-190 MHz, independent of the Low-Band detection.