Observationally-Motivated Mass Outflow Rates
Massive stars power galactic outflows which remove gas from star-forming regions and regulate star formation. The actual amount of mass that outflows remove from galaxies sensitively determines how much gas and metals that they retain and their subsequent evolution. Measuring the mass outflow rate is crucial to determine how effectively massive stars shape galaxy evolution. 

Typically, uncertain assumptions for the ionization structure, gas-phase metallicity, and geometry must be made to determine mass outflow rates. In a series of papers, I demonstrated how the FUV metal absorption lines can be used to constrain many of these quantities to determine observationally-motivated prescriptions of the mass outflow rates.
The figure on the right shows the scaling of the mass-loading factor (the mass outflow rate divided by the star formation rate) with stellar mass. The mass-loading factor measures how efficiently outflows remove gas from the galaxy relative to the formation of stars. At low-masses, outflows remove 10 times more gas than the galaxies form into stars! At higher stellar masses the outflows are more pedestrian, such that only 10-20% of the gas that could form into stars is removed. This means that low-mass galaxies inefficiently form stars and eject much more gas out of their galaxies. Meanwhile, high-mass galaxies retain more gas as stars and can build up their baryons. 
Simulations often times scale sub-scale prescriptions of the massive star feedback using the mass-loading factor. The figure to the left shows how the observed mass-loading factors compare to two representative simulations. The observed mass-loading factors are smaller than the simulations, but they have very similar scalings as the simulations. The difference could be that my observations do not probe all of the outflowing gas (different temperature phases), or maybe the simulations drive too strong of galactic outflows. This would impact the amount of gas available for the galaxies form into stars and would drastically impact their star formation histories.
The combination of the mass outflow rate and the outflow velocity determines the change of the momentum with time. The momentum deposition equals the net force on the outflowing gas. The net force on the gas is the sum of forces, mainly the outward (positive) force imparted by the star formation and the inward gravitational tug from the mass within the galaxy. The plot to the right shows that the observed outflow momentum deposition is entirely consistent with the net forces acting on the outflow (the points lie along the one-to-one line). This fundamentally illustrates that the energy and momentum from massive stars is sufficient to remove gas from galaxies.

This mass outflow rates have important implications for the observed mass-metallicity trends, but the question may be: What do these absorption lines represent, physically? Follow the buttons to answer those questions!