Collaborative Research: Observing the Cosmic Evolution of Neutral Hydrogen

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Hydrogen is the most abundant element in the universe, and neutral hydrogen atoms are thus an important constituent of interstellar gas in galaxies ? but also one of the most challenging to study. The faintness of neutral hydrogen emission means that it can only be detected beyond the nearby universe via long observations with large telescopes. A new telescope with improved sensitivity, the MeerKAT array, will examine how galaxies' neutral gas reservoirs have evolved over two thirds of the universe's history (i.e., the last nine billion years of cosmic time). It will determine how galaxies' neutral atomic hydrogen content relates to the properties of their stars, their environments, and their cosmic epochs. This will be compared with theoretical predictions in order to understand how gas flows into and out of galaxies and forms new stars while inside galaxies. The research will support the training of graduate and undergraduate students at the four universities; graduate students will gain additional experience in computation and statistics, research mentorship, education in STEM disciplines, and outreach to a variety of audiences.This survey will probe neutral hydrogen (HI) in emission to an unprecedentedly high redshift of z = 1.45. The combination of individual and stacked HI detections ? complemented by theoretical modelling, multiwavelength observations, and a rich z = 0 reference dataset ? will probe the evolution of (i) the baryonic Tully-Fisher relation, (ii) the HI mass function, and (iii) the dependence of galaxies' HI content on stellar and dark matter properties. OH megamasers detected as strong line emitters in the MeerKAT data will be used to place constraints on the cosmic history of gas-rich galaxy mergers. Both the HI survey data and the instructional modules used to provide student training will be publicly released as part of the project.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.