Properties of Ionized Outflows in Galaxy Mergers

Galaxy interactions and feedback mechanisms are, separately, known to play crucial roles in the evolution of galaxies. Galaxy mergers can drive dramatic morphological changes, trigger bursts of star formation, and increase accretion onto the central supermassive black hole. Outflowing gas and dust can provide positive or negative feedback; outflows may compress previously undisturbed gas and trigger star formation (positive feedback), or may evacuate large deposits of gas and subsequently quench star formation (negative feedback). Despite the importance of both mechanisms, there are currently no large-scale systematic studies of outflows in galaxy mergers. To address this deficiency, we have conducted the first large-scale systematic study of outflows in mergers compared to a carefully constructed control sample of isolated galaxies. We use the [OIII] λ5007 emission line to trace ionized outflows in a sample of galaxies drawn from the Sloan Digital Sky Survey. In addition to comparing the incidence and properties of outflows in mergers and controls, we also examine how these properties depend on merger stage. We find that outflows are much rarer in star-forming galaxies compared to AGN, and there is a positive correlation between outflow incidence and velocity with galaxy luminosity. Further, outflows are more common in mid-infrared selected AGN at all luminosities compared to optically selected AGN. Lastly, we find no statistically significant difference in outflow properties and incidence between mergers and controls. These results suggest that the merging environment does not have a significant impact on large-scale ionized gas outflows, and that luminosity and AGN selection technique are important in shaping outflow properties, at least as traced by the [OIII] λ5007 line.