Quantifying the AGN-driven outflows in ULIRGs (QUADROS) IV: HST/STIS
  spectroscopy of the sub-kpc warm outflow in F14394+5332
  Considerable uncertainties remain about the nature of warm, AGN-driven
outflows and their impact on the evolution of galaxies. This is because the
outflows are often unresolved in ground-based observations. As part of a
project to study the AGN outflows in some of the most rapidly evolving galaxies
in the local Universe, here we present HST/STIS observations of F14394+5332E
that resolve the sub-kpc warm outflow for the first time in a ULIRG. The
observations reveal a compact, high-ionization outflow region (r_max~0.9 kpc)
set in a more extensive (r_max~1.4 kpc) halo that is kinematically quiescent
and has a lower ionization state. A large line width (600 < FWHM < 1500 km/s)
is measured throughout the outflow region, and the outflowing gas shows a steep
velocity gradient with radius, with the magnitude of the blueshifted velocities
increasing from ~500 to 1800 km/s from the inner to the outer part of the
outflow. We interpret the observations in terms of the local acceleration, and
hydrodynamic destruction, of dense clouds as they are swept up in a hot, low
density wind driven by the AGN. We discuss the implications for measuring the
mass outflow rates and kinetic powers for the AGN-driven outflows in such
objects.
