Gas and star formation in the extreme environments of starburst galaxies

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In the universe around us, galaxies are made up of billions of stars, many with planets circling around them. This means that we must first understand how stars form before we can understand the formation of either galaxies or planets. My research program focuses on nearby galaxies that are currently experiencing an intense burst of star formation, turning gas into stars at rates that are 10-100 times faster than the rate in galaxies like our own Milky Way. Specifically, I study the physical properties of the gas that is the fuel for star formation, in order to understand why the star formation in these galaxies has kicked into overdrive. Although these "starburst galaxies" are now relatively rare, these high rates of star formation were normal in the early universe, when young galaxies rich in gas were forming most of the stars we see today. However, because these young galaxies lie at incredibly large distances, even the most powerful telescopes find it extremely difficult to measure the detailed properties that are needed for comparison with simulations of star and galaxy formation. Nearby starburst galaxies provide the opportunity to probe the extreme environments (high densities of gas and star formation) that were common in the early universe, but now on the scales of a few hundred light years that are required to provide strong tests of star formation models. My research team will use data from a powerful radio telescope, the Atacama Large Millimeter/submillimeter Array (ALMA), to attack the problem of star formation in extreme environments along several fronts. (1) We will compare rates of star formation with the amount of available gas to probe the universality of the physics that underpins the empirical "star formation law" that has been established for galaxies like our own Milky Way. (2) We will make the first detailed measurements of the populations of individual giant gas clouds in starburst galaxies. Changes in cloud properties may explain the intense star formation: for example, higher density clouds will collapse faster, which could drive the gas to form stars more rapidly. (3) We will also use these new cloud catalogs to obtain critical calibrations that are needed to turn our radio images of galaxies into accurate measurements of the mass of gas in those galaxies. (4) In the most extreme starburst galaxies in the local universe, galaxies so rich in gas and dust that their centres are completely hidden from view in visible light, we will use rarer molecular isotopes (such as 12C18O instead of 12C16O) to probe how long the starbursts last and what kinds of stars they form. Overall, this program of research will provide a breakthrough in our understanding of star formation in the most extreme environments in the universe today and will have strong impact on our understanding of the main epoch of galaxy formation in early universe.