  Emission-line studies in the active galactic nuclei (AGNs), particularly
those utilizing high spatial resolution, provide the most accurate method to
determine critical quantities of the central engine and of the gas a few tens
of parsecs away. Using seeing-limited data with spectroscopy, we have explored
the extended narrow-line region for a sample of active galactic nuclei (AGNs)
with strong, forbidden emission lines that have high-ionization potentials (IP
$\gtrsim$ 100 eV). We have studied the optical and near-infrared spectra for
these AGNs, extracted and compared their spectral energy distributions, and put
constraints on the physical conditions of the region producing the coronal
lines. We have realized a novel black hole mass scaling relation with one such
prominent coronal line - [Si VI] 1.963 microns, over the 10$^6$ - 10$^8$
M$_{\odot}$ interval, that suggests photoionization by the continuum produced
by the accretion disk is the primary physical process at play here. We perform
a detailed parameter space study to optimize the emission from these coronal
lines in terms of fundamental black hole parameters and test predictions that
can be used to measure the kinematics of the extended X-ray emission gas. With
the successful launch and first light of the JWST, we are well-poised to refine
our findings using the superb angular resolution of the telescope that will
allow us to map the inner few parsecs to the central supermassive black holes.
This opens up the study of the higher ionization lines that will be spatially
resolved by JWST, expanding our sample to tens of hundreds of AGNs, and putting
firmer constraints on the physical conditions in the coronal line region.
