The Unique Challenges Facing Studies of the 21-cm Signal at 55 > z

Abstract: Observations of the redshifted 21-cm signal emitted and absorbed by neutral hydrogen is one of the most promising tools to enable the next generation of cosmological discovery. The 21-cm signal can in principle be studied over 13 billion years of cosmic history, making it a distinctly powerful tracer of the universe’s growth. However, there are vast challenges facing experiments seeking to observe the 21-cm signal; it is not only many orders of magnitude smaller than Galactic foregrounds, but the frequencies over which it can be studied are heavily occupied by RFI. While sharing these challenges, experiments conducting observations of the 21-cm signal targeting different periods of the universe’s history demand vastly different experimental designs which pose unique instrumental challenges. The speaker will provide an overview of his work related to two experiments in 21-cm cosmology: the Canadian Hydrogen Observatory and Radio transient Detector (CHORD), a 21-cm intensity mapping experiment targeting the epoch of dark energy domination, and the Mapper of the IGM Spin Temperature (MIST), a global 21-cm experiment targeting the cosmic dawn era. Hendriksen will describe the key differences in the designs of each experiment, and how their unique instrumental challenges are approached.