Alex Reda successfully defends thesis, "Beam Calibration for the Canadian Hydrogen Intensity Mapping Experiment"
On July 17, Alex Reda successfully defended the thesis, “Beam Calibration for the Canadian Hydrogen Intensity Mapping Experiment” (Advisor: Laura Newburgh).
Reda explained, “We have known for about a century that the Universe is expanding, but more recently it was discovered that the expansion is accelerating. This is unexpected and not easily explained by known physics, so to understand why this is happening, we need better measurements of the overall expansion rate of the Universe over time. To make these kinds of measurements, we try to map the distribution of matter in the Universe and measure how that distribution is stretched out over time as the Universe expands. With CHIME (the Canadian Hydrogen Intensity Mapping Experiment), we aim to do this by looking for the glow of hydrogen atoms, the simplest and most abundant element in the Universe.”
Reda continued, “The main difficulty with these measurements is that the hydrogen we’re looking for produces a very dim signal in a very bright sky, so my thesis project focused primarily on expanding and improving our methods to understand how CHIME sees the sky so we can identify and remove the contaminants in our data and isolate just the glow of cosmic hydrogen. My methods have given us a way to understand some features of the instrument that cannot be measured using other techniques, and this will be key as CHIME’s data analysis enters an advanced phase where instrument calibration is more important.”
Reda will next be a postdoc at Boston University, working on SPT-SLIM, a mm-wave line intensity mapping pathfinder for the South Pole Telescope (SPT).
Thesis Abstract: Intensity mapping of the 21 cm line of neutral hydrogen is a promising new approach to charting the large scale structure of the Universe. The Canadian Hydrogen Intensity Mapping Experiment (CHIME) has played a crucial role in establishing the observational viability of this probe, recently achieving the first independent detection of the cosmological 21 cm power spectrum at redshift z ∼1. However, this detection is insensitive to the baryon acoustic oscillation (BAO) scale, a known standard ruler in cosmology whose evolution over cosmic time CHIME was built to measure to constrain the expansion history of the Universe and the underlying physics of dark energy. The large scales sensitive to BAO are obscured by bright astrophysical foregrounds which are 4-5 orders of magnitude brighter than the 21 cm signal; characterizing and removing these foregrounds requires exquisite control of the telescope beam response, which imprints spurious spectral structure on otherwise smooth foreground emission. I present a project which adapts the classic radio holography technique to address the challenge of beam calibration for a large telescope using stationary cylindrical reflectors.
Thesis committee: Laura Newburgh (Advisor), Nikhil Padmanabhan, Karsten Heeger, Laura Havener, Laura Wolz (The University of Manchester)