The Physics of the Coronal Line Region for Galaxies in MaNGA
  The fundamental nature and extent of the coronal line region (CLR), which may
serve as a vital tracer for Active Galactic Nucleus (AGN) activity, remain
unresolved. Previous studies suggest that the CLR is produced by AGN-driven
outflows and occupies a distinct region between the broad line region and the
narrow line region, which places it tens to hundreds of parsecs from the
galactic center. Here, we investigate 10 coronal line (CL; ionization potential
$\ge$ 100 eV) emitting galaxies from the SDSS-IV MaNGA catalog with emission
from one or more CLs detected at $\ge$ $5{\sigma}$ above the continuum in at
least 10 spaxels - the largest such MaNGA catalog. We find that the CLR is far
more extended, reaching out to 1.3 - 23 kpc from the galactic center. We
cross-match our sample of 10 CL galaxies with the largest existing MaNGA AGN
catalog and identify 7 in it; two of the remaining three are galaxy mergers and
the final one is an AGN candidate. Further, we measure the average CLR electron
temperatures to range between 12,331 K - 22,530 K, slightly above the typical
threshold for pure AGN photoionization ($\sim$ 20,000 K) and indicative of
shocks (e.g., merger-induced or from supernova remnants) in the CLR. We reason
that ionizing photons emitted by the central continuum source (i.e. AGN
photoionization) primarily generate the CLs, and that energetic shocks are an
additional ionization mechanism that likely produce the most extended CLRs we
measure.
