Infrared Spectral Energy Distribution and Variability of Active Galactic Nuclei: Clues to the Structure of Circumnuclear Material

TL;DR

This paper reviews how infrared observations of active galactic nuclei reveal the structure and variability of circumnuclear dust, offering insights into black hole growth and galaxy evolution.

Contribution

It synthesizes current IR observational data on AGN spectral energy distributions and variability, providing a comprehensive understanding of their circumnuclear structures.

Findings

IR SEDs vary with AGN luminosity and redshift

Dust emission responds to central engine variability

Insights into obscuring structures and host galaxy IR properties

Abstract

The active galactic nucleus (AGN) phenomena results from a supermassive black hole accreting its surrounding gaseous and dusty material. The infrared (IR) regime provides most of the information to characterize the dusty structures that bridge from the galaxy to the black hole, providing clues to the black hole growth and host galaxy evolution. Over the past several decades, with the commissioning of various ground, airborne and space IR observing facilities, our interpretations of the AGN circumnuclear structures have advanced significantly through improved understanding of how their dust emission changes as a function of wavelength and how the heating of the dusty structures responds to variations of the energy released from the central engine. In this review, we summarize the current observational knowledge of the AGN IR broad-band spectral energy distributions (SEDs) and the IR time variability behavior covering large ranges of AGN luminosity and redshift, and discuss some first-order insights into the obscuring structures and host galaxy IR properties that can be obtained by integrating the relevant observations into a coherent picture.