Constraints on the spin temperature of intergalactic hydrogen at a redshift of z = 8.4, derived from upper limits on the 21 cm signal measured by PAPER. Gray regions are excluded at 95% confidence. At this redshift, the spin temperature is equivalent to the physical (kinetic) temperature of the gas. These limits rule out “cold reionization” scenarios, requiring sources of energy to heat the intergalactic medium.

My research is in the field of 21 cm cosmology, which uses low frequency radio astronomy to explore the history of the universe.  By observing the highly redshifted hyperfine (21 cm) line of neutral hydrogen, one can make a three-dimensional map spanning cosmic history, from the dark ages to relatively recent times.  Depending on the epoch being probed, these observations can be used to study dark energy, the physics of early galaxy and star formation, and potentially even probe the primordial conditions of the universe during the inflationary epoch.  Because of the challenges to recovering this information — such as terrestrial radio interference and Galactic foreground emission — these studies utilize specialized radio telescope experiments specifically designed for 21 cm cosmology work.

Although I have been involved in nearly all aspects of the 21 cm cosmology community, my current principal contributions to the field lie at the interface between data analysis and cosmology.  I focus on using the latest algorithms in foreground isolation and removal to characterize the challenges facing these experiments and explore their effects on recovering the scientific signal.  Using these lessons, I have also designed a novel 21 cm experiment targeting a measurement of dark energy: the BAO Broadband and Broad-beam (BAOBAB) array.  Lately, I have also focused on how to use preliminary upper limits from 21 cm experiments to constrain the physics of reionization.