Galactic Outflows

This shows the rotating disk and outflowing gas in an ultra Luminous Infrared Galaxy.

Our current working theory for the evolution of galaxies suggests that large galaxies evolve through major merger events, where two galaxies of similar sizes collide. This chaotic and energetic process produces a lot of dust, and causes “bursts” of star-formation. Simulations and observations of these “Ultra Luminous” galaxies (called ULIRGs, or Ultra-Luminous Infrared Galaxies) suggest that they are very effective at forming stars creating much larger, less chaotic galaxies.

However, we still don’t understand how to prevent stars from forming. Observational evidence suggests that massive galaxies stop forming stars quite early in the history of the universe. There must be some mechanism by which the raw materials that form stars (cold Hydrogen gas) are expelled from large galaxies.

At the same time, we can see that gas in these “ULIRGs” is moving at high velocities away from the center of the galaxy. These outflows are good candidate mechanism to remove the cold, star-forming gas from massive galaxies. My research focuses on observing the very central regions of these ULIRGs, and understanding the mechanisms which launch this outflowing gas. We try to differentiatie between gas launched from the central supermassive black hole1 and gas launched due to stars in the center of the galaxy.

I use the OSIRIS spectrograph at Keck, an adaptive optics based instrument to study the gas expelled from these ULIRGs. Along with our understanding of the gas in the central regions of these galaxies, we can also use OSIRIS to measure the mass of the super-massive black hole.

  1. These galaxies have black holes which weigh in at millions and billions of suns. These supermassive black holes (similar to the relatively small one at the center of our galaxy) are spinning, and taking in gas. As part of this process, additional gas is expelled along very linear jets.