Evolving Gas Chemistry and Star Formation in Local Galaxies

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In this project, the relationship between chemistry and star formation is studied by analyzing molecular line emissions from complexes of giant molecular clouds in a sample of nearby galaxies. This is done with high spatial resolution astrochemical observations at cm and mm wavelengths using the Combined Array for Research in Millimeter-Wave Astronomy (CARMA) and the Institut de Radio Astronomie Millimétrique? (IRAM) interferometers. Main targets are the inner bulges of local galaxies that show different structural and star formation properties. The diagnostics from astrochemistry and morphological studies can shed light on the regulating mechanisms of galaxy evolution. This work looks for the chemical changes that are introduced in the molecular composition of the interstellar medium by star formation and large scale dynamics, or vice versa, it identifies chemical tracers for these processes. Some gas species are known as tracers of particular processes, but may be difficult to observe. Other, easier observable molecules can serve as proxies for the molecules that are difficult to observe, but more of these need to be identified. The observations provide molecular line lists that serve as pathfinder for the coming observations with the Atacama Large Millimeter Array (ALMA) and Expanded Very Large Array (EVLA). Specifically, the chemistry is used to deconstruct the energetics and substructure of shocks by analyzing the changes in large-scale distribution of ejected grain species. A second application is to investigate the slopes of Schmidt-Kennicutt star formation law and their sensitivities for a given chemical tracer. A third study analyzes changes in the state of molecular gas in star-forming regions where photo-dissociation is important.The broader impact of this work is its strong astrochemical focus. The list of important molecular tracers for the various large-scale environments is a useful asset for the community as ALMA and EVLA observations are coming closer. Other fields such as galactic dynamics and stellar evolution also benefit from the identification of tracers of shock structure and stellar feedback. The graduate student who participates in this project will be well trained to be an active ALMA and EVLA user. As part of this project, a "powers of chemistry" poster series for high schools and colleges is developed which describes the role of chemistry over a wide range of scales and the chemistry from this work clearly spans the largest dimensions. It is hoped that this helps to attract students to pursue scientific careers.