Apples to Apples: Comparing the Cores of Nearby Galaxies

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The centers of galaxies are home to unique interactions between stars, gas, and black holes. Such interactions are responsible for forming new stars, growing a galaxy's central supermassive black hole, and driving energetic outflows. However, the detailed physics behind them is still poorly understood. Though nearby and easily studied, the Milky Way's center is relatively quiet. Few stars are forming in this region, and the black hole is not active. Because of this, the Milky Way is not a representative example of the full suite of processes that occur in these environments. This project will make the first comparison of gas properties in the Milky Way center with those in a more active galaxy. This work will lead to advances in our understanding of how the physics of the gas in galaxy centers is linked to inflow and outflow processes. In addition, this work will support a partnership with a prison education program to develop and teach math-intensive astronomy courses that will prepare incarcerated students to be part of a STEM-literate workforce. A key area of investigation, and a priority identified in the 2010 Decadal Survey, is what goes on in galaxy centers: the interactions between stars, black holes and gas. Until recently there has only been one galaxy where these interactions can be investigated in detail: The Milky Way, an inactive and relatively sedate galaxy. Now however, the capabilities offered by the Atacama Large Millimeter Array (ALMA) make it possible to conduct detailed comparisons of gas properties and interactions in the Milky Way center with those in other galaxy centers. Using new radio and millimeter observations of the Milky Way's Galactic center, this project will first make detailed studies of gas properties to constrain how accretion itself modifies gas conditions, and not just feedback from processes it drives (e.g., starbursts which are absent in the Galactic center). By relating the gas properties on sub-parsec scales determined by this study (scales that can only be probed in our own Galaxy center) to the properties on the parsec and larger scales, this work will test how well global properties probed in other galaxies represent the true properties on smaller scales. Ultimately, this project will directly compare the properties on parsec scales with new ALMA observations of the nearest starburst galaxy on identical parsec scales. Their work is the first 'apples to apples' comparison of detailed gas properties in galaxy nuclei: probing how interstellar medium properties change in the presence of a starburst, and advancing the understanding of our Galaxy center beyond a single case study. Finally, this program will produce a library of templates for the extreme gas properties in these nuclei that can be used to interpret conditions in distant, high redshift galaxies.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.