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.
This is a preview of subscription content, access via your institution
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Get time limited or full article access on ReadCube.
All prices are NET prices.
Salpeter, E. E. Accretion of interstellar matter by massive objects. Astrophys. J. 140, 796–800 (1964)
Lynden-Bell, D. Galactic nuclei as collapsed old quasars. Nature 223, 690–694 (1969)
Shields, G. A. Thermal continuum from accretion disks in quasars. Nature 272, 706–708 (1978)
Malkan, M. A. The ultraviolet excess of luminous quasars. II - Evidence for massive accretion disks. Astrophys. J. 268, 582–590 (1983)
Shakura, N. I. & Sunyaev, R. A. Black holes in binary systems. Observational appearance. Astron. Astrophys. 24, 337–355 (1973)
Antonucci, R. in High Energy Processes in Accreting Black Holes (Astron. Soc. Pacif. Conf. Ser. 161) (eds Poutanen, J. & Svensson, R.) 193–203 (Astronomical Society of the Pacific, San Francisco, 1999)
Koratkar, A. & Blaes, O. The ultraviolet and optical continuum emission in active galactic nuclei: the status of accretion disks. Publ. Astron. Soc. Pacif. 111, 1–30 (1999)
Hubeny, I., Agol, E., Blaes, O. & Krolik, J. H. Non-LTE models and theoretical spectra of accretion disks in active galactic nuclei. III. Integrated spectra for hydrogen-helium disks. Astrophys. J. 533, 710–728 (2000)
Neugebauer, G. et al. Continuum energy distributions of quasars in the Palomar-Green Survey. Astrophys. J. Suppl. Ser. 63, 615–644 (1987)
Cristiani, S. & Vio, R. The composite spectrum of quasars. Astron. Astrophys. 227, 385–393 (1990)
Francis, P. J. et al. A high signal-to-noise ratio composite quasar spectrum. Astrophys. J. 373, 465–470 (1991)
Zheng, W., Kriss, G. A., Telfer, R. C., Grimes, J. P. & Davidsen, A. F. A. Composite HST spectrum of quasars. Astrophys. J. 475, 469–479 (1997)
Vanden Berk, D. E. et al. Composite quasar spectra from the Sloan Digital Sky Survey. Astron. J. 122, 549–564 (2001)
Sanders, D. B., Phinney, E. S., Neugebauer, G., Soifer, B. T. & Matthews, K. Continuum energy distribution of quasars - Shapes and origins. Astrophys. J. 347, 29–51 (1989)
Davis, S. W., Woo, J.-H. & Blaes, O. M. The UV continuum of quasars: Models and SDSS spectral slopes. Astrophys. J. 668, 682–698 (2007)
Malkan, M. in Theory of Accretion Disks (NATO ASIC Proc. 290) (ed. Meyer, F.) 19–28 (Kluwer Academic, Norwell, Massachusetts, 1989)
Malkan, M. A. & Filippenko, A. V. The stellar and nonstellar continua of Seyfert galaxies: Nonthermal emission in the near-infrared. Astrophys. J. 275, 477–492 (1983)
Antonucci, R. R. J. Optical polarization position angle versus radio structure axis in Seyfert galaxies. Nature 303, 158–159 (1983)
Smith, J. E. et al. A spectropolarimetric atlas of Seyfert 1 galaxies. Mon. Not. R. Astron. Soc. 335, 773–798 (2002)
Smith, J. E. et al. Seyferts on the edge: polar scattering and orientation-dependent polarization in Seyfert 1 nuclei. Mon. Not. R. Astron. Soc. 350, 140–160 (2004)
Kishimoto, M., Antonucci, R. & Blaes, O. A first close look at the Balmer-edge behaviour of the quasar big blue bump. Mon. Not. R. Astron. Soc. 345, 253–260 (2003)
Kishimoto, M., Antonucci, R., Boisson, C. & Blaes, O. The buried Balmer edge signatures from quasars. Mon. Not. R. Astron. Soc. 354, 1065–1092 (2004)
Webb, W., Malkan, M., Schmidt, G. & Impey, C. The wavelength dependence of polarization of active galaxies and quasars. Astrophys. J. 419, 494–514 (1993)
Impey, C. D., Malkan, M. A., Webb, W. & Petry, C. E. Ultraviolet spectropolarimetry of high-redshift quasars with the Hubble Space Telescope. Astrophys. J. 440, 80–90 (1995)
Kishimoto, M., Antonucci, R. & Blaes, O. The dust-eliminated shape of quasar spectra in the near-infrared: a hidden part of the big blue bump. Mon. Not. R. Astron. Soc. 364, 640–648 (2005)
Bentz, M. C., Peterson, B. M., Pogge, R. W., Vestergaard, M. & Onken, C. A. The radius-luminosity relationship for active galactic nuclei: the effect of host-galaxy starlight on luminosity measurements. Astrophys. J. 644, 133–142 (2006)
Blaes, O. M. in Accretion Discs, Jets and High Energy Phenomena in Astrophysics (eds Beskin, V. et al.) 137–185 (Springer, Berlin, 2003)
Agol, E. & Krolik, J. H. Magnetic stress at the marginally stable orbit: Altered disk structure, radiation, and black hole spin evolution. Astrophys. J. 528, 161–170 (2000)
Shlosman, I. & Begelman, M. C. Self-gravitating accretion disks in active galactic nuclei. Nature 329, 810–812 (1987)
Goodman, J. Self-gravity and quasi-stellar object discs. Mon. Not. R. Astron. Soc. 339, 937–948 (2003)
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.
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)
About this article
Cite this article
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
This article is cited by
Space Science Reviews (2014)
Frontiers of Physics (2013)