The Physical Conditions and Scaling Relations of Multi-Phase Galactic Outflows

Star formation injects energy and momentum into the interstellar medium, accelerating the gas outward in a galaxy-scale outflow. These outflows eject large amounts of gas out of star-forming regions, helping to control the number of stars formed in a galaxy. In this thesis, I present new observational studies of galactic outflows in the local universe that describe the physical conditions of outflows and how the physical conditions scale with host galaxy properties. I find shallow, yet statistically significant, scaling relations between the outflow velocity and both the star formation rate and the stellar mass of their host galaxies. These scaling relations describe the acceleration of gas out of galaxies, and provide constraints for galaxy evolution models. In particular, I find that low-mass galaxies (stellar mass less than 1010.5 M[special character omitted]) generate low-ionization outflows faster than their escape velocities, while high-mass galaxies generally do not, unless they are merging with another galaxy. I then explore a variety of ionic transitions that probe the different ionization stages of the outflow. The outflow velocity of each transition depends on the strength of the transition, and I model the outflows as a single co-moving phase. Photo-ionization models determine the ionization structure and metallicities of the outflows. For the local merger NGC 6090, I combine these ionization models with detailed fits to the optical depth and covering fraction of the Si IV absorption lines. These fits determine how the velocity, density, covering fraction and mass outflow rate scales with distance from the starburst. Finally, I study the molecular outflow of M 82 using three different CO emission lines. I model the temperature and density of the molecular gas to estimate the total molecular mass outflow rate, without relying on uncertain conversion factors. I compare the mass outflow rate to the star formation rate and an estimate of the inflow rate to characterize the molecular baryon cycle of M 82. Taken as a whole, this thesis explores the physical properties of nearby galactic outflows, studying how these physical properties scale with host galaxy properties. These results describe the efficiency of star formation, and the cycling of gas out galaxies.