The view of AGN-host alignment via reflection spectroscopy

TL;DR

This study uses reflection spectroscopy to analyze the alignment between the inner accretion disc of AGN and their host galaxy's stellar disc, revealing complex feeding mechanisms and potential warping effects.

Contribution

It introduces a novel method of using reflection fits to determine AGN disc inclination and compares it with host galaxy orientation, highlighting the impact of unmodeled features and sample heterogeneity.

Findings

No significant correlation between inner disc and host galaxy inclination for the full sample.

Removing a small subset reveals a possible 1:1 correlation, suggesting diverse feeding mechanisms.

Evidence for some AGN being fueled by minor mergers or exhibiting disc warping effects.

Abstract

The fuelling of active galactic nuclei (AGN) - via material propagated through the galactic disc or via minor mergers - is expected to leave an imprint on the alignment of the sub-pc disc relative to the host galaxy's stellar disc. Determining the inclination of the inner disc usually relies on the launching angle of the jet; here instead we use the inclination derived from reflection fits to a sample of AGN. We determine the distorting effect of unmodeled Fe XXV/XXVI features and, via extensive simulations, determine the difference in disc inclination resulting from the use of relxill compared to reflionx. We compare inner disc inclinations to those for the host galaxy stellar disc derived from the Hubble formula and, via Monte-Carlo simulations, find a strong lack of a correlation (at >> 5-sigma) implying either widespread feeding via mergers if we assume the sample to be homogeneous, or that radiative disc warps are distorting our view of the emission. However, we find that by removing a small (~1/5) subset of AGN, the remaining sample is consistent with random sampling of an underlying 1:1 correlation (at the 3-sigma level). A heterogenous sample would likely imply that our view is not dominated by radiative disc warps but instead by different feeding mechanisms with the majority consistent with coplanar accretion (although this may be the result of selection bias), whilst a smaller but not insignificant fraction may have been fuelled by minor mergers in the recent history of the host galaxy.