Galactic outflow

A galactic outflow carries gas, metals, energy, and momentum away from a galaxy under stellar or active-galactic-nucleus feedback. Whether the material escapes or later returns depends on its speed and the galactic potential.

The mass-loading factor is the ratio of outflow rate to star-formation rate, $\lambda ={\dot{M}}_{\mathrm{out}}/{\dot{M}}_{\ast }$. Its value can depend on galaxy mass, radius, gas phase, and the surface through which the flow is measured.