MSI Seminar

New Directions in Galaxy Formation and Cosmology Following the EDGES 78 MHz Detection

Jordan Mirocha

McGill University

On March 1st of last year, the EDGES collaboration reported the detection of a sharp absorption signal in the all-sky radio spectrum at ~78 MHz. This frequency is roughly consistent with early theoretical predictions for the global 21-cm signal, a sky-averaged spectral signature of neutral hydrogen atoms in the intergalactic medium before cosmic reionization. However, the reported amplitude is ~2.5 times larger than the strongest possible global 21-cm signal in standard cosmological models. This startling feature of the EDGES signal has led to a variety of exotic explanations, including milli-charged dark matter and as-yet-unidentified radio backgrounds in the early Universe, both of which can amplify 21-cm absorption signals relative to standard expectations. In this talk, I will first highlight the flurry of ideas that have arisen in the last ~year to explain the anomalous amplitude of the EDGES signal. Then, I will turn to an under-appreciated aspect of the signal: its timing is not consistent with empirically-calibrated models of high-z galaxies. If confirmed, the EDGES signal may thus be evidence of new physics *and* new astrophysics.