Are there reliable methods to estimate the nuclear orientation of Seyfert galaxies?

TL;DR

This study evaluates four methods for estimating the nuclear inclination of Seyfert galaxies, finding that [O iii] mapping is the most reliable, supporting the Unified Model at certain scales but noting potential complexities closer to the black hole.

Contribution

It compares and assesses the reliability of four different methods to determine the nuclear orientation of AGN, highlighting the effectiveness of [O iii] mapping.

Findings

[O iii] mapping shows strong correlations with inclination-dependent observables.

The Unified Model is supported at kiloparsec to sub-parsec scales.

Warping and misalignments may occur within 0.01 pc of the black hole.

Abstract

Orientation, together with accretion and evolution, is one of the three main drivers in the Grand Unification of Active Galactic Nuclei (AGN). Being unresolved, determining the true inclination of those powerful sources is always difficult and indirect, yet it remains a vital clue to apprehend the numerous, panchromatic and complex spectroscopic features we detect. There are only a hundred inclinations derived so far; in this context, can we be sure that we measure the true orientation of AGN? To answer this question, four methods to estimate the nuclear inclination of AGN are investigated and compared to inclination-dependent observables (hydrogen column density, Balmer linewidth, optical polarization, and flux ratios within the IR and relative to X-rays). Among these orientation indicators, the method developed by Fisher, Crenshaw, Kraemer et al., mapping and modeling the radial velocities of the [O iii] emission region in AGN, is the most successful. The [O iii]-mapping technique shows highly statistically significant correlations at >95% confidence level for rejecting null hypothesis for all the test cases. Such results confirm that the Unified Model is correct at a scale ranging from kiloparsec to a fraction of a parsec. However, at a radial distance less than 0.01 pc from the central black hole, warps and misalignments may change this picture.