A novel black hole mass scaling using coronal lines in active galaxies
  Using bonafide black hole (BH) mass estimates from reverberation mapping and
the line ratio [Si VI]1.963$\mu$m/Br$\gamma_{\rm broad}$ as tracer of the
Active Galactic Nuclei (AGN) ionizing continuum, we find a novel BH-mass
scaling relation of the form log($M_{\rm BH}) = (6.40\pm 0.17) - (1.99\pm 0.37)
\times$ log ([Si VI]/Br$\gamma_{\rm broad})$, over the BH mass interval, $10^6
- 10^8$ M$_{\odot}$. The current sample consists of 21 Type-1 AGNs with the
overall dispersion in our scaling relation at 0.47 dex, one that emulates the
well-established M-$\sigma$ relation which shows a dispersion $\sim$0.44 dex.
The new scaling offers an economic, and physically motivated alternative for BH
estimate using single epoch spectra, avoiding large telescope time
(reverberation mapping) or absolute flux calibration (the continuum luminosity
method). With the advent of big surveys in the infrared in the near future, we
aim to reduce the scatter in the relation by supplementing with more sources.
