A Holistic View of Gas, Dust, and Metals in Galaxies

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The gas between stars is part of the interstellar medium (ISM) and is fundamental to understanding how galaxies evolve. However, the gas often can only be studied by indirect methods, and the most widely used tracer is emission from carbon monoxide (CO). This project will advance the understanding of CO and dust as tracers, using new observations of nearby galaxies from the Hubble Space Telescope, the Atacama Large Millimeter/submillimeter Array, and other facilities. The team will study the CO emission from the ISM of the Magellanic Clouds, as well as the ISM in the centers of nearby galaxies. They will conduct a series of summer workshops designed to help transfer students moving from community colleges to UC San Diego. Transfer students are a diverse, highly motivated group, disadvantaged by the compressed timeline after transferring, and removing these barriers is a key step in broadening the participation of under-represented groups. Indirect methods are needed because most of the hydrogen molecules are too cold to produce emission lines. Calibrating CO emission as a tracer requires understanding several parameters: the dust-to-gas ratio as a function of metallicity, the relation between dust emission and dust mass at a given temperature, and the conversion between CO and hydrogen, all of which vary with conditions in the ISM. The new observations will be brought together to create an applicable prescription for dust emissivity, dust-to-gas ratio, and conversion factor, as a function of environment. This will allow assessment of the ISM gas content over the full range from the Milky Way to distant high-redshift galaxies, and help to remove inescapable systematic uncertainties intrinsic to the current approach. The work should yield new insights into the physical state of the ISM in galaxies, including the arrangement of molecular clouds and their response to galactic environment.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.