The Mass Inflow and Outflow Rates of the Milky Way
  We present new calculations of the mass inflow and outflow rates around the
Milky Way, derived from a catalog of ultraviolet metal-line high velocity
clouds (HVCs). These calculations are conducted by transforming the HVC
velocities into the Galactic Standard of Rest (GSR) reference frame,
identifying inflowing (v_GSR < 0 km/s) and outflowing (v_GSR > 0 km/s)
populations, and using observational constraints on the distance, metallicity,
dust content, covering fractions, and total hydrogen column density of each
population. After removing HVCs associated with the Magellanic Stream and the
Fermi Bubbles, we find inflow and outflow rates in cool (T~10^4 K) ionized gas
of dM_in/dt >~ 0.53+/-0.17 (d/12 kpc) (Z/0.2 Z_sun)^-1 M_sun/yr and dM_out/dt
>~ 0.16+/-0.06 (d/12 kpc) (Z/0.5 Z_sun)^-1 M_sun/yr. The excess of inflowing
over outflowing gas suggests that the Milky Way is currently in an
inflow-dominated phase, but the presence of substantial mass flux in both
directions supports a Galactic fountain model, in which gas is constantly
recycled between the disk and the halo. We also find that the metal flux in
both directions (in and out) is indistinguishable. By comparing the outflow
rate to the Galactic star formation rate, we present the first estimate of the
mass loading factor (etc_HVC) of the disk-wide Milky Way wind, finding eta_HVC
>~ 0.10+/-0.06 (d/12 kpc) (Z/0.5 Z_sun)^-1. Including the contributions from
low- and intermediate-velocity clouds and from hot gas would increase these
inflow and outflow estimates.
