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The characteristic blue spectra of accretion disks in quasars as uncovered in the infrared

Nature volume 454, pages 492–494 (2008)Cite this article

Abstract

Quasars are thought to be powered by supermassive black holes accreting surrounding gas1,2,3. Central to this picture is a putative accretion disk which is believed to be the source of the majority of the radiative output2,3,4. It is well known, however, that the most extensively studied disk model5—an optically thick disk which is heated locally by the dissipation of gravitational binding energy—is apparently contradicted by observations in a few major respects6,7. In particular, the model predicts a specific blue spectral shape asymptotically from the visible to the near-infrared5,8, but this is not generally seen in the visible wavelength region where the disk spectrum is observable9,10,11,12,13. A crucial difficulty has been that, towards the infrared, the disk spectrum starts to be hidden under strong, hot dust emission from much larger but hitherto unresolved scales, and thus has essentially been impossible to observe. Here we report observations of polarized light interior to the dust-emitting region that enable us to uncover this near-infrared disk spectrum in several quasars. The revealed spectra show that the near-infrared disk spectrum is indeed as blue as predicted. This indicates that, at least for the outer near-infrared-emitting radii, the standard picture of the locally heated disk is approximately correct.

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Figure 1: Overlay of the polarized- and total-light spectra observed in six different quasars.
Figure 2: Spectral index of polarized light spectra.

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Acknowledgements

The UK Infrared Telescope (UKIRT) is operated by the Joint Astronomy Centre on behalf of the Science and Technology Facilities Council of the UK. We thank the Department of Physical Sciences, University of Hertfordshire, for providing the IRPOL2 polarimetry facility for the UKIRT. This research is partially based on observations collected at the European Southern Observatory, Chile.

Author information

Authors and Affiliations

  1. Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany ,

    Makoto Kishimoto

  2. Scottish Universities Physics Alliance, Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK ,

    Makoto Kishimoto & Andy Lawrence

  3. Physics Department, University of California, Santa Barbara, California 93106, USA,

    Robert Antonucci, Omer Blaes & Christian Leipski

  4. LUTH, FRE 2462 du CNRS, associée à l'Université Denis Diderot, Observatoire de Paris, Section de Meudon, F–92195 Meudon Cedex, France ,

    Catherine Boisson

  5. Instituto de Astronomía, Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta 1270709, Chile ,

    Marcus Albrecht

Authors
  1. Makoto Kishimoto
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  2. Robert Antonucci
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  3. Omer Blaes
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  4. Andy Lawrence
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  5. Catherine Boisson
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  6. Marcus Albrecht
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  7. Christian Leipski
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Corresponding author

Correspondence to Makoto Kishimoto.

Supplementary information

Supplementary information

The file contains Supplementary Notes, Supplementary Figures 1-8 and Supplementary Tables 1-8. This Supplementary Information contains details on observations and data reductions, and also on the removal of instrumental polarization. (PDF 1683 kb)

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Kishimoto, M., Antonucci, R., Blaes, O. et al. The characteristic blue spectra of accretion disks in quasars as uncovered in the infrared. Nature 454, 492–494 (2008). https://doi.org/10.1038/nature07114

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