The Quest to Detect 21cm fluctuations from X-ray sources before Reionization

by Dr Aaron Ewall-Wice (UC Berkeley)

Thursday 9 Apr 2020, 15:00 → 16:00 US/Eastern

Two important chapters in our Universe’s history remain, for the most part, unexplored by direct observations. During the “dark ages”, cooling gas clouds left over from the big bang collapsed into dark-matter halos to form the first bound objects and where conditions were right, the first stars ignited, heralding in the “Cosmic Dawn”. These first generations of galaxies heated, ionized, and enriched the intergalactic medium, forever changing the nature of stars and galaxies that could form in the future. Unfortunately, the majority of sources that drove this transformation are too faint to detect directly with optical and infrared facilities any time soon. A promising avenue to illuminating the cosmic dawn is to observe the impact of early sources on 21cm emission from the abundant HI that existed before reionization. Today, a number of radio facilities are being commissioned to detect the redshifted HI signal.  

I will present an overview of 21cm experiments along with the systematics challenges that they face and the strategies being adopted to overcome these challenges including the adoption of spectrally smooth RF signal chains and novel calibration techniques. I will also report progress by the Hydrogen Epoch of Reionization Array (HERA) in realizing these strategies.  

I will finish with a discussion of work exploring whether the recently claimed detection of a 78MHz cosmic dawn absorption feature by EDGEs might be explained by rapidly accreting radio loud black holes in the early Universe and the potential of power spectrum measurements by HERA to check whether the absorption feature is cosmological.