“The Origin of Multiphase Galaxy Outflows”

Star-forming galaxies are often observed to host galactic winds – gas that is flowing out of the galaxy in phases ranging from cold molecular clouds to hot X-ray emitting plasma. While these multiphase outflows are routinely observed, theoretically constraining their origin and evolution has proven difficult. Explaining the prevalence and velocities of the cool ionized phase (T~10^4 K) in particular poses a challenge. In this talk, I will discuss a potential dual origin for this cool gas. Through a series of extremely high-resolution simulations run with the GPU-based Cholla code, I will show that in high star formation surface density systems, dense disk gas can be pushed out by the collective effect of clustered supernovae, explaining the low-velocity material. Subsequent shredding and mixing of these clouds creates gas with intermediate densities and temperatures that is prone to radiative cooling, allowing momentum to transfer between phases and producing high velocity cool gas. In addition to explaining the nature of outflows themselves, these multiphase winds could potentially be a source of the cool photo-ionized gas that is found in abundance in galaxy halos.