Coronal Line Forest AGN I: physical properties of the emission-line
  regions
  Coronal-Line Forest Active Galactic Nuclei (CLiF AGN) are characterized by
strong high-ionization lines, which contrast to what is found in most AGNs.
Here, we carry out a multiwavelength analysis aimed at understanding the
physical processes in the Narrow Line Region (NLR) of these objects and
unveiling if they are indeed a special class of AGN. By comparing coronal
emission-line ratios we conclude that there are no differences between CLiF and
non-CLiF AGNs. We derive physical conditions of the narrow line region (NLR)
gas and found electron densities in the range $3.6\times$10$^{2}$ -
$1.7\times$10$^{4}$ cm$^{-3}$ and temperatures of $3.7\times$10$^{3}$ -
$6.3\times$10$^{4}$ K, suggesting that the ionization mechanism is associated
primarily with photoionization by the AGN. We suggest a NLR dominated by
matter-bounded clouds to explain the high-ionization line spectrum observed.
The mass of the central black hole, derived from the stellar velocity
dispersion show that most of the objects have values in the interval
10$^{7-8}$~M$\odot$. Our results imply that CLiF AGN is not a separate category
of AGNs. In all optical/near-infrared emission-line properties analyzed, they
represent an extension to the low/high ends of the distribution within the AGN
class.
