Coronal Line Forest AGN I: physical properties of the emission-line regions

TL;DR

This study investigates Coronal-Line Forest AGN, revealing they are not a distinct class but rather an extension of typical AGN properties, with similar physical conditions and black hole masses, primarily driven by photoionization.

Contribution

It provides a comprehensive multiwavelength analysis of CLiF AGN, showing they share properties with non-CLiF AGN and are not a separate category, expanding understanding of AGN diversity.

Findings

CLiF AGN have similar emission-line ratios to non-CLiF AGN.

NLR electron densities range from 360 to 17,000 cm$^{-3}$.

Black hole masses mostly between 10$^{7}$ and 10$^{8}$ solar masses.

Abstract

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.