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Active galactic nuclei as seen by the Spitzer Space Telescope

Nature Astronomy volume 4, pages 352–363 (2020)Cite this article

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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 at optical or X-ray wavelengths. 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. Spitzer’s sensitivity 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 programmes with new and upcoming infrared facilities.

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Fig. 1: The torus model.
Fig. 2: Spectroscopic diagnostics of the mid-infrared emission from AGNs.
Fig. 3: The connection between an AGN and its host, as seen in the mid-infrared.
Fig. 4: Comparison of mid-infrared AGN selection techniques to results from the X-ray.
Fig. 5: The mid-infrared luminosity function of AGNs from combined Spitzer and WISE results.

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Acknowledgements

We thank the dedicated staff at the Spitzer Science Center and the members of the Instrument Teams who made Spitzer successful. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

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  1. National Radio Astronomy Observatory, Charlottesville, VA, USA

    Mark Lacy

  2. Tufts University, Medford, MA, USA

    Anna Sajina

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Lacy, M., Sajina, A. Active galactic nuclei as seen by the Spitzer Space Telescope. Nat Astron 4, 352–363 (2020). https://doi.org/10.1038/s41550-020-1071-x

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