AGN Obscuration and the Unified Model

TL;DR

This paper reviews the evidence for obscuring media in active galactic nuclei across multiple scales, challenging the traditional torus model and proposing a more complex unification scenario.

Contribution

It provides an updated overview of the geometrical distribution of obscuring media in AGN, integrating recent observational results to refine the unification model.

Findings

Evidence for multi-scale obscuring media

Need for complex geometrical models

Challenges to the traditional torus paradigm

Abstract

Unification Models of Active Galactic Nuclei postulate that all the observed differences between Type 1 and Type 2 objects are due to orientation effects with respect to the line-of-sight to the observer. The key ingredient of these models is the obscuring medium, historically envisaged as a toroidal structure on a parsec scale. However, many results obtained in the last few years are clearly showing the need for a more complex geometrical distribution of the absorbing media. In this paper we review the various pieces of evidence for obscuring media on different scales, from the vicinity of the black hole to the host galaxy, in order to picture an updated unification scenario explaining the complex observed phenomenology. We conclude by mentioning some of the open issues.