Tracking X-ray Outflows with Optical/IR Footprint Lines
  We use Cloudy photoionisation models to predict the flux profiles for
optical/IR emission lines that trace the footprint of X-ray gas, such as [Fe X]
6375A and [Si X] 1.43$\mu$m. These are a subset of coronal lines, from ions
with ionisation potential $\geq$ that of O VII, i.e., 138eV. The footprint
lines are formed in gas over the same range in ionisation state as the H and
He-like of O and Ne ions, which are also the source of X-ray emission lines.
The footprint lines can be detected with optical and IR telescopes, such as the
Hubble Space Telescope/STIS and James Webb Space Telescope/NIRSpec, and can
potentially be used to measure the kinematics of the extended X-ray emission
gas. As a test case, we use the footprints to quantify the properties of the
X-ray outflow in the Seyfert 1 galaxy NGC 4151. To confirm the accuracy of our
method, we compare our model predictions to the measured flux from archival
STIS spectra and previous ground-based studies, and the results are in good
agreement. We also use our X-ray footprint method to predict the mass profile
for the X-ray emission-line gas in NGC 4151 and derive a total
spatially-integrated X-ray mass of $7.8(\pm 2.1) \times 10^{5}~M_{\odot}$, in
comparison to $5.4(\pm 1.1) \times 10^{5}~M_{\odot}$ measured from a Chandra
X-ray analysis. Our results indicate that high-ionisation footprint emission
lines in the optical and near-infrared can be used to accurately trace the
kinematics and physical conditions of AGN ionised, X-ray emission-line gas.
