Active Galactic Nuclei as seen by the Spitzer Space Telescope

TL;DR

The Spitzer Space Telescope significantly advanced the understanding of Active Galactic Nuclei by revealing obscured populations, dust properties, and host galaxy characteristics through mid-infrared observations, informing future infrared studies.

Contribution

This paper highlights how Spitzer's capabilities uncovered obscured AGNs, detailed dust and gas features, and improved host galaxy identification, providing insights for future infrared missions.

Findings

Revealed a substantial population of highly-obscured AGNs.

Identified silicate features and shocked gas in AGN environments.

Enabled near-complete host galaxy identification of AGNs.

Abstract

The Spitzer Space Telescope revolutionized studies of Active Galactic Nuclei (AGNs). Its combined sensitivity and mapping speed at mid-infrared wavelengths revealed a substantial population of highly-obscured AGNs. This population implies a higher radiative accretion efficiency, and thus possibly a higher spin for black holes than indicated by surveys in the optical and X-ray. The unique mid-infrared spectrographic capability of Spitzer gave important insights into the distribution and nature of the dust surrounding AGNs, enabling the separation of AGN and starburst components, the detection of silicate features in emission from hot dust, and the identification of shocked gas associated with AGN activity. The sensitivity of Spitzer allowed almost complete identification of the host galaxies of samples of AGNs selected in the X-ray and radio. As we look forward to the James Webb Space Telescope, the lessons learned from Spitzer studies will inform observational programs with new and upcoming infrared facilities.