On the Unification of Active Galactic Nuclei

TL;DR

This paper challenges the traditional unification model of active galactic nuclei (AGNs) by showing that their observed differences are due to a preference in the distribution of torus covering factors, not intrinsic distinctions.

Contribution

It demonstrates that AGNs are drawn preferentially from the distribution of torus covering factors, with type 2 AGNs more likely from higher end, impacting unification models.

Findings

Type 2 AGNs have higher IR luminosity.

Type 2 AGNs show more Compton thick X-ray obscuration.

Type 1 and 2 AGNs are not intrinsically the same, but distribution-dependent.

Abstract

The inevitable spread in properties of the toroidal obscuration of active galactic nuclei (AGNs) invalidates the widespread notion that type 1 and 2 AGNs are intrinsically the same objects, drawn randomly from the distribution of torus covering factors. Instead, AGNs are drawn \emph{preferentially} from this distribution; type 2 are more likely drawn from the distribution higher end, type 1 from its lower end. Type 2 AGNs have a higher IR luminosity, lower narrow-line luminosity and a higher fraction of Compton thick X-ray obscuration than type 1. Meaningful studies of unification statistics cannot be conducted without first determining the intrinsic distribution function of torus covering factors.