Collaborative Research: Cosmology with CHIME

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The Canadian Hydrogen Intensity Mapping Experiment (CHIME) will help understand dark energy by mapping out the distribution of matter throughout the Universe. One of the greatest mysteries in science is that the expansion of the Universe is currently accelerating, implying that a mysterious dark energy permeates the Universe and pushes on it. The discovery of dark energy resulted in a Nobel Prize, but its nature is no clearer today than it was 20 years ago. In fact, more recent measurements have led to less certainty, with different measurements of exactly how fast the Universe is expanding. CHIME is a new radio telescope designed to measure distant galaxies through the radio emission of neutral hydrogen gas that resides within them. In order to measure the hydrogen emission, other bright radio signals from our own galaxy and other sources must be removed. This foreground removal requires a precise understanding of the CHIME instrument itself. This project will measure the instrument, improve nuisance radio emission removal, and combine the CHIME measurements with galaxy catalogues to make a measurement of dark energy. The program will also develop education-oriented radio receivers that will be used in STEM programs at MIT, WVU and Yale. Radio receivers for education have been developed through a partnership between WVU and the Green Bank Observatory to teach teachers the digital signal processing techniques necessary to build a digital spectrometer.Analysis will be undertaken that cross-correlates 21cm maps from CHIME with optical galaxy survey data from eBOSS to measure the large-scale structure (LSS) of the Universe. CHIME is designed to measure neutral hydrogen associated with galaxies at redshifts from 0.8 to 2.5, producing constraints on dark energy over a critical redshift range that is difficult to probe statistically with optical galaxy surveys alone. To make this measurement bright foreground emission from our own galaxy and extragalactic sources must be removed, which places stringent requirements on instrument calibration. In this program the researchers will attempt to measure the expansion history through: (i) improved instrument beam modelling, (ii) demonstrated foreground removal techniques, and (iii) the measurement of large-scale structure with 21cm emission in cross-correlation with eBOSS optical galaxies.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.