Illuminating the Dark Universe with Radio Observations

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I propose to develop a research program in observations of redshifted 21-cm emission of neutral hydrogen that will shed new light on uncharted territory in the universe's history. Hydrogen is the most abundant element in the universe and is an extremely powerful tool for probing the universe's distant past. Neutral hydrogen atoms naturally emit light with a wavelength of 21 cm, and this light is stretched or "redshifted" because of the expansion of the universe. By measuring the sky at radio frequencies, it is possible to access specific epochs of the universe's history by selecting the appropriate observational wavelengths.******My research program will address two major themes. The first goal is to probe the nature of dark energy, a bizarre component of the universe that is causing the expansion rate to accelerate. A promising technique for tackling this challenge is using 21-cm emission from galaxies to make a three-dimensional map of the distribution of matter. The matter distribution encodes ripples ("baryon acoustic oscillations") with a characteristic length scale that can be used as a "ruler" for charting the expansion history of the universe and pinpointing the growth spurt caused by dark energy. Large, highly sensitive radio telescope arrays are required to make these measurements, and there are unique challenges associated with the design, implementation, and operation of these instruments. My program will involve the development of novel hardware designs for redundant interferometric radio telescope arrays, as well as specialized techniques for precise characterization of these arrays. The second goal of my research program is to lay the groundwork for future explorations of the cosmic dark ages. This epoch, which occurred after the universe cooled sufficiently for neutral hydrogen atoms to form (~400,000 years after the big bang) is unexplored to date and represents one of the final observational frontiers in cosmology. There is a potential wealth of information to be mined from this era, but corresponding 21-cm observations at these frequencies are exceptionally difficult because of the brightness of the Milky Way, ionospheric effects, and terrestrial radio-frequency emission. Nevertheless, recent observations suggest that low-frequency (<30 MHz) measurements may be accessible from carefully selected locations and with modern technological developments. My program will involve the development of radically new instrument designs for low-frequency telescope arrays and data analysis for a low-frequency pathfinder system that my team and I recently installed.******My overall program will be multi-faceted and will bring together instrument design, characterization, integration, and analysis. In addition to delivering high-impact science, my program will provide excellent training for HQP to develop a wide range of experimental research and leadership skills that are critical for opening new discovery space in cosmology.