CHIME Wins 2024 Buchalter Cosmology Prize

January 16, 2025
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UBC (former) grad student Meiling Deng on CHIME

Press release by the CHIME Collaboration, Jan, 2025

The CHIME Collaboration has been named the first-place winner of the 2024 Buchalter Cosmology Prize for measuring the clustering of hydrogen gas over a large region of the observable universe.  The prize recognizes “ground-breaking theoretical, observational, or experimental work in cosmology that has the potential to produce a breakthrough advance in our understanding.”

The winning paper, “Detection of Cosmological 21 cm Emission with the Canadian Hydrogen Intensity Mapping Experiment” (see here: https://arxiv.org/pdf/2202.01242), was praised by the Buchalter Prize judging panel as “a promising approach to mapping the large-scale structure of the universe and the first step towards measuring the baryon acoustic oscillations in the power spectrum of 21 cm emission, which is expected to improve our understanding of the nature of dark energy.”

Hydrogen atoms naturally emit electromagnetic radiation with a wavelength of 21 cm, a phenomenon predicted by quantum mechanics.

Through the last 13 billion years of cosmic history, the vast majority of atomic hydrogen has been concentrated in the outskirts of galaxies, and we therefore expect that these galaxies will give off a faint “glow” of 21 cm radiation.  By measuring the brightness of this glow over large areas of the sky, radio telescopes on Earth can map the distribution of galaxies: regions where galaxies are more densely packed emit more radiation, while regions with fewer galaxies emit less.

The radiation’s wavelength is stretched (or “redshifted”) by the expansion of the universe, with the amount of stretching depending on the distance between the source and the observer.  As a result, measurements at wavelengths greater than 21 cm tell us about galaxies farther away.  By making measurements at many different wavelengths, radio telescopes can use this stretching to obtain a 3-dimensional map of the distribution of galaxies, via a technique known as “21 cm intensity mapping.”

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a radio telescope that was purpose-built for this technique.  In its prize-winning paper, the CHIME Collaboration used data from the telescope (located at the Dominion Radio Astrophysical Observatory in British Columbia, Canada) to measure the statistical correlation between the brightness of its sky maps and the positions of galaxies measured by the Sloan Digital Sky Survey.  CHIME’s high-significance measurement of this correlation is the first such measurement made with an instrument that was custom-built for intensity mapping.  At the time of publication, it was also the highest-redshift 21 cm intensity mapping measurement ever made (a record which has since been surpassed by a later analysis of CHIME data).

CHIME is  located on the traditional, ancestral, and unceded territory of the syilx people and benefits enormously from the radio frequency interference protection work by the syilx Okanagan Nation and the DRAO.

The DRAO staff have been enormously helpful to this project.

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