Nuclear Outflow of the Milky Way: Studying the Kinematics and Spatial
  Extent of the Northern Fermi Bubble
  We report new observations from a systematic, spectroscopic, ultraviolet
absorption-line survey that maps the spatial and kinematic properties of the
high-velocity gas in the Galactic Center region. We examine the hypothesis that
this gas traces the biconical nuclear outflow. We use ultraviolet spectra of 47
background QSOs and halo stars projected inside and outside the northern Fermi
Bubble from the Hubble Space Telescope to study the incidence of high velocity
absorption around it. We use five lines of sight inside the northern Fermi
Bubble to constrain the velocity and column densities of outflowing gas traced
by O I, Al II, C II, C IV, Si II, Si III, Si IV and other species. All five
lines of sight inside the northern Fermi Bubble exhibit blueshifted high
velocity absorption components, whereas only 9 out of the 42 lines of sight
outside the northern Fermi Bubble exhibit blueshifted high velocity absorption
components. The observed outflow velocity profile decreases with Galactic
latitude and radial distance (R) from the Galactic Center. The observed
blueshifted velocities change from $v_{GSR}$=-265 km/s at R~2.3 kpc to
$v_{GSR}$=-91 km/s at R~6.5 kpc. We derive the metallicity of the entrained gas
along the 1H1613-097 sightline, which passes through the center of the northern
Fermi Bubble, finding [O/H] $\gtrsim -0.54 \pm 0.15$. A simple kinematic model
tuned to match the observed absorption component velocities along the five
lines of sight inside the Bubble, constrains the outflow velocities to
~1000$-$1300 km/s, and the age of the outflow to be ~ 6$-$9 Myr. We estimate a
minimum mass outflow rate for the nuclear outflow to be $\gtrsim$ 0.2 $\rm{
M_{\odot}\; yr^{-1}}$. Combining the age and mass outflow rates, we determine a
minimum mass of total UV absorbing cool gas entrained in the Fermi Bubbles to
be $\gtrsim \rm{ 2 \times 10^{6} M_{\odot}}$.
