  Intermediate mass black holes (IMBHs), with masses between 100 to 10^5
M_\odot, represent the link between stellar mass black holes and the
supermassive black holes that reside in galaxy centers. While IMBHs are crucial
to our understanding of black hole seed formation, black holes of less than
\approx 10^4 M_\odot eluded detection by traditional searches. Observations of
the infrared coronal lines (CLs) offer us one of the most promising tools to
discover IMBHs in galaxies. We have modeled the infrared emission line spectrum
that is produced by gas photoionized by an AGN radiation field and explored for
the first time the dependence of the infrared CL spectrum on black hole mass
over the range of 10^2 M_\odot to 10^8 M_\odot. We show that infrared CLs are
expected to be prominent in the spectra of accreting IMBHs and can potentially
be a powerful probe of the black hole mass in AGNs. We identify key emission
line ratios in the 1-30 \mu m range that are most sensitive to black hole mass.
While variations in accretion rate and the physical parameters of the gas can
also affect the CL spectrum, we demonstrate that the effect of black hole mass
is likely to be the most dramatic over the mass range explored in our models.
With the unprecedented sensitivity of JWST, a large number of CLs will be
detectable for the first time, providing important insight into the existence
and properties of IMBHs in the local universe, potentially revolutionizing our
understanding of this class of object.
