Astrophysics Seminar

The emergence of cosmic acceleration—the increasingly rapid expansion of the Universe since redshift ∼1.5—has signaled either that gravitationally repulsive dark energy dominates the energy density of the universe today or that Einstein's general relativity does not correctly describe gravity on cosmological scales. Nature has provided a standard ruler with which to measure the expansion history of the universe: the baryon acoustic oscillation (BAO) scale. The impact of this discovery on fundamental physics and astrophysics is revolutionary, and decoding the physics of cosmic acceleration requires new, higher-quality measurements of the expansion rate of the universe as a function of time. A novel technique to probe large-scale structures throughout cosmic history is by hydrogen  21-cm intensity mapping (IM). By mapping the 3D distribution of matter across vast cosmic volumes, we can test competing explanations for dark energy and dark matter. However, a dedicated instrument is required to survey a large volume of sky quickly to measure cosmic acceleration with the sensitivity required to test dark energy models.

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a drift-scan radio interferometer located at the Dominion Radio Astrophysical Observatory (DRAO) in Penticton, British Columbia, Canada. CHIME, operating between 400 and 800 MHz, will map the redshifted 21-cm emission of neutral hydrogen between redshifts z = 0.8 − 2.5 across the northern sky. The CHIME collaboration has already reported the detection of the cosmological 21-cm signal in cross-correlation with the eBOSS survey. However, measuring the cosmological 21-cm signal is challenging due to bright astrophysical foregrounds, which are about 4-5 orders of magnitude brighter than the cosmological HI signal, coupled with chromatic instrument response and emission from terrestrial sources. I will discuss methodologies developed to address these issues and the improvements made in the data processing to measure the cosmological 21-cm signal. I will discuss our progress toward measuring the cosmological 21-cm auto-power spectrum.

The Canadian Hydrogen Observatory and Radio-transient Detector (CHORD) is a next-generation radio interferometer, located at the DRAO, Canada. CHORD will consist of  512 dishes of 6m diameter arranged in a compact redundant array, operating between 300 to 1500 MHz. Using bandwidth × field of view × sensitivity as a figure of merit, CHORD will be an order of magnitude more powerful than CHIME and become the world-leading facility of its type. CHORD will map the 3D distribution of matter, using 21-cm intensity mapping, between redshift 0 to 3.7, revolutionizing our understanding of dark energy and its evolution. Additionally, CHORD will detect millions of individual galaxies through their 21-cm emission. In this presentation, I will provide an overview of the experiment, highlighting the science goals and forecasted cosmological constraints.