Coronal-Line Forest AGN: the best view of the inner edge of the AGN torus?

Abstract

We introduce Coronal-Line Forest active galactic nuclei (CLiF AGN), AGN which have a rich spectrum of forbidden high-ionization lines (FHILs, e.g. [Fe VII], [Fe X] and [Ne V]), as well as relatively strong narrow (300 km s -1 ) H emission when compared to the other Balmer transition lines. We find that the kinematics of the CLiF emitting region are similar to those of the forbidden low-ionization emission-line (FLIL) region. We compare emission line strengths of both FHILs and FLILs to CLOUDY photoionization results and find that the CLiF emitting region has higher densities (10 4.5 < n H < 10 7.5 cm -3 ) when compared to the FLIL emitting region (10 3.0 < n H < 10 4.5 cm -3 ). We use the photoionization results to calculate the CLiF regions radial distances (0.04 < R CLiF < 32.5 pc) and find that they are comparable to the dust grain sublimation distances (0.10 < R SUB < 4.3 pc). As a result, we suggest that the inner torus wall is the most likely location of the CLiF region, and the unusual strength of the FHILs is due to a specific viewing angle giving a maximal view of the far wall of the torus without the continuum being revealed.