New Constraints on Feedback from a Comprehensive Study of Galactic Winds

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AST-0907839TremontiThis award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The influence of massive stars and accreting black holes on the surrounding interstellar medium, termed 'feedback', has been regarded as an important ingredient of galaxy evolution since the 1970s. Feedback regulates star formation by heating cold clouds which would otherwise form stars, and by inserting kinetic energy which can drive gas out of the galaxy disk, and possibly completely out of the potential well. Although some form of feedback is included in all modern numerical simulations, understanding of the complex interplay between the baryonic constituents of galaxies is still woefully incomplete. However, some of the best empirical constraints come from the study of galactic-scale gaseous outflows, or 'galactic winds'. This project will support a thesis student for the most ambitious and comprehensive study of galactic winds to date, detecting outflows both by direct imaging of extra-planar ionized gas in a sample of edge-on disk galaxies, and through absorption-line spectroscopy of nearly face-on galaxies. The study will map the dependence of observables on key physical properties of the host galaxies, such as stellar mass, star formation rate, star formation surface density, black hole mass, active galactic nucleus luminosity, and local environment. Spectral and spatial information will be combined to infer the wind energetics and the mass outflow rates. These data will supply critical information on the efficiency of feedback, and new benchmarks for numerical models of galaxy evolution. The impressively deep images of outflows in the H-alpha light of ionized hydrogen will provide a focal point for public outreach, and will be used in public talks to demonstrate the physics behind a 'pretty picture'.