Intermediate Inclinations of Type 2 Coronal-Line Forest AGN

TL;DR

This study investigates the inclination angles of Type 2 Coronal-Line Forest AGN using mid-infrared colors, supporting the idea that their unique spectral features are due to intermediate viewing angles of the AGN torus.

Contribution

It provides evidence that CLiF AGN have intermediate inclination angles, confirming their position in the AGN unification model based on mid-IR color analysis.

Findings

CLiF AGN have intermediate IR colors between Type 1 and Type 2 AGN.

Supports the hypothesis that spectral features are inclination-dependent.

CLiF AGN are valuable for studying AGN unification.

Abstract

Coronal-Line Forest Active Galactic Nuclei (CLiF AGN) are remarkable in the sense that they have a rich spectrum of dozens of coronal emission lines (e.g. [FeVII], [FeX] and [NeV]) in their spectra. Rose, Elvis & Tadhunter (2015) suggest that the inner obscuring torus wall is the most likely location of the coronal line region in CLiF AGN, and the unusual strength of the forbidden high ionization lines is due to a specific AGN-torus inclination angle. Here we test this suggestion using mid-IR colours (4.6$\mu$m-22$\mu$m) from the Wide-Field Infrared Survey Explorer (WISE) for the CLiF AGN. We use the Fischer et al. (2014) result that showed that as the AGN-torus inclination becomes more face on, the Spitzer 5.5$\mu$m to 30$\mu$m colours become bluer. We show that the [W2-W4] colours for the CLiF AGN ($\langle$[W2-W4]$\rangle$ = 5.92$\pm$0.12) are intermediate between SDSS type 1 ($\langle$[W2-W4]$\rangle$ = 5.22$\pm$0.01) and type 2 AGN ($\langle$[W2-W4]$\rangle$ = 6.35$\pm$0.03). This implies that the AGN-torus inclinations for the CLiF AGN are indeed intermediate, supporting the work of Rose, Elvis \& Tadhunter (2015). The confirmed relation between CLiF AGN and their viewing angle shows that CLiF AGN may be useful for our understanding of AGN unification.