New Directions in Galaxy Formation and Cosmology Following the First High-z 21-cm Detection

On March 1st, the EDGES collaboration reported the detection of a sharp absorption signal in the all-sky radio spectrum at ~80 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 in principle 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 ~six months 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.

Speaker: Jordan Mirocha, Mcgill University