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The obscuration by dust of most of the growth of supermassive black holes


Supermassive black holes underwent periods of exponential growth during which we see them as quasars in the distant Universe. The summed emission from these quasars generates the cosmic X-ray background, the spectrum of which has been used to argue that most black-hole growth is obscured1,2. There are clear examples of obscured black-hole growth in the form of ‘type-2’ quasars3,4,5, but their numbers are fewer than expected from modelling of the X-ray background. Here we report the direct detection of a population of distant type-2 quasars, which is at least comparable in size to the well-known unobscured type-1 population. We selected objects that have mid-infrared and radio emissions characteristic of quasars, but which are faint at near-infrared and optical wavelengths. We conclude that this population is responsible for most of the black-hole growth in the young Universe and that, throughout cosmic history, black-hole growth occurs in the dusty, gas-rich centres of active galaxies.

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Figure 1: Diagrammatic representation of the infrared selection criteria.
Figure 2: Probability distributions for the quasar fraction.


  1. 1

    Worsley, M. A., Fabian, A. C., Barcons, X., Mateos, S. & Hasinger, G. The (un)resolved X-ray background in the Lockman Hole. Mon. Not. R. Astron. Soc. 354, 720–726 (2004)

    Article  Google Scholar 

  2. 2

    Fabian, A. C. The obscured growth of massive black holes. Mon. Not. R. Astron. Soc. 308, L39–L43 (1999)

    ADS  CAS  Article  Google Scholar 

  3. 3

    Antonucci, R. Unified models for active galactic nuclei and quasars. Annu. Rev. Astron. Astrophys. 31, 473–521 (1993)

    ADS  CAS  Article  Google Scholar 

  4. 4

    Rowan-Robinson, M. et al. A high-redshift IRAS galaxy with huge luminosity—hidden quasar or protogalaxy? Nature 351, 719–721 (1991)

    ADS  Article  Google Scholar 

  5. 5

    Norman, C. et al. A classic Type 2 quasar. Astrophys. J. 571, 218–225 (2002)

    ADS  Article  Google Scholar 

  6. 6

    Wolf, C. et al. The evolution of faint AGN between z1 and z5 from the COMBO-17 survey. Astron. Astrophys. 408, 499–514 (2003)

    ADS  Article  Google Scholar 

  7. 7

    Willott, C. J., Rawlings, S., Blundell, K. M. & Lacy, M. The quasar fraction in low-frequency-selected complete samples and implications for unified schemes. Mon. Not. R. Astron. Soc. 316, 449–458 (2000)

    ADS  Article  Google Scholar 

  8. 8

    Baker, J. C. et al. Associated absorption in radio quasars. I. C IV absorption and the growth of radio sources. Astrophys. J. 568, 592–609 (2002)

    ADS  CAS  Article  Google Scholar 

  9. 9

    Barger, A. J. et al. The cosmic evolution of hard X-ray-selected active galactic nuclei. Astron. J. 129, 578–609 (2005)

    ADS  CAS  Article  Google Scholar 

  10. 10

    Zakamska, N. L. et al. Candidate type II quasars from the SDSS: III. Spectropolarimetry reveals hidden type I nuclei. Astron. J. (in the press)

  11. 11

    Zheng, W. et al. Photometric redshifts of X-ray sources in the Chandra Deep Field South. Astrophys. J. Suppl. Ser. 155, 73–87 (2004)

    ADS  Article  Google Scholar 

  12. 12

    Alexander, D. M. et al. A Chandra observation of the z = 2.285 galaxy FSC10214 + 4724: Evidence for a Compton-thick quasar? Mon. Not. R. Astron. Soc. 357, L16–L20 (2005)

    ADS  Article  Google Scholar 

  13. 13

    Broadhurst, T. & Lehar, J. A gravitational lens solution for the IRAS Galaxy FSC 10214 + 4724. Astrophys. J. 450, L41–L44 (1995)

    ADS  Article  Google Scholar 

  14. 14

    Serjeant, S. et al. A spectroscopic study of IRAS F10214 + 4724. Mon. Not. R. Astron. Soc. 298, 321–331 (1998)

    ADS  CAS  Article  Google Scholar 

  15. 15

    Werner, M. W. et al. The Spitzer Space Telescope Mission. Astrophys. J. Suppl. Ser. 154, 1–9 (2004)

    ADS  Article  Google Scholar 

  16. 16

    Croom, S. M. et al. The 2dF QSO Redshift Survey-XII. The spectroscopic catalogue and luminosity function. Mon. Not. R. Astron. Soc. 349, 1397–1418 (2004)

    ADS  Article  Google Scholar 

  17. 17

    Lacy, M. et al. The Infrared Array Camera component of the Spitzer Space Telescope Extragalactic First Look Survey. Astrophys. J. Suppl. Ser. (in the press)

  18. 18

    Condon, J. J. et al. The SIRTF First-Look survey. I. VLA image and source catalog. Astrophys. J. 125, 2411–2426 (2003)

    Google Scholar 

  19. 19

    Chapman, S. C., Blain, A. W., Smail, I. & Ivison, R. J. A redshift survey of the submillimetre galaxy population. Astrophys. J. 622, 772–796 (2005)

    ADS  CAS  Article  Google Scholar 

  20. 20

    Rawlings, S., Eales, S. & Warren, S. The detection of four high-redshift (0.5 ≤ z ≤ 3.22) radiogalaxies by optical spectroscopy of five blank fields. Mon. Not. R. Astron. Soc. 243, 14–18 (1990)

    ADS  Google Scholar 

  21. 21

    Alexander, D. M. et al. Rapid growth of black holes in massive star-forming galaxies. Nature 434, 738–740 (2005)

    ADS  CAS  Article  Google Scholar 

  22. 22

    Cirasuolo, M., Celotti, A., Magliocchetti, M. & Danese, L. Is there a dichotomy in the radio loudness distribution of quasars? Mon. Not. R. Astron. Soc. 346, 447–455 (2003)

    ADS  Article  Google Scholar 

  23. 23

    Miller, P., Rawlings, S. & Saunders, R. The radio and optical properties of the z < 0.5 BQS quasars. Mon. Not. R. Astron. Soc. 263, 425–460 (1993)

    ADS  CAS  Article  Google Scholar 

  24. 24

    Treister, E. et al. Obscured AGN and the X-ray, optical and far-infrared number counts of AGN in the GOODS fields. Astrophys. J. 616, 123–135 (2004)

    ADS  CAS  Article  Google Scholar 

  25. 25

    Lawrence, A. The relative frequency of broad-lined and narrow-lined active galactic nuclei—implications for unified schemes. Mon. Not. R. Astron. Soc. 252, 586–592 (1991)

    ADS  CAS  Article  Google Scholar 

  26. 26

    Simpson, C. A new look at the isotropy of narrow-line emission in extragalactic radio sources. Mon. Not. R. Astron. Soc. 297, L39–L43 (1998)

    ADS  CAS  Article  Google Scholar 

  27. 27

    Simpson, C. The luminosity dependence of the type 1 active galactic nucleus fraction. Mon Not. R. Astron. Soc. 360, 565–572 (2005)

    ADS  CAS  Article  Google Scholar 

  28. 28

    Yu, Q. & Tremaine, S. Observational constraints on growth of massive black holes. Mon. Not. R. Astron. Soc., 965–976 (3352002)

  29. 29

    Marleau, F. R. et al. Extragalactic source counts at 24 microns in the Spitzer First Look survey. Astrophys. J. Suppl. Ser. 154, 66–69 (2004)

    ADS  CAS  Article  Google Scholar 

  30. 30

    Bruzual, G. & Charlot, S. Stellar population synthesis at the resolution of 2003. Mon. Not. R. Astron. Soc. 344, 1028 (2003)

    Article  Google Scholar 

  31. 31

    Rowan-Robinson, M. A new model for the infrared emission of quasars. Mon. Not. R. Astron. Soc. 272, 737–748 (1995)

    ADS  Google Scholar 

  32. 32

    Pei, Y. C. Interstellar dust from the Milky Way to the Magellanic Clouds. Astrophys. J. 395, 130–139 (1992)

    ADS  Article  Google Scholar 

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We thank C. Wolf, L. Clewley, H.-R. Klöckner and G. Cotter for discussions. A.M.-S. is grateful to the Council of the European Union for financial support. S.R. and C.S. are grateful to the UK PPARC for a Senior Research Fellowship and an Advanced Fellowship respectively.

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Correspondence to Alejo Martínez-Sansigre.

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Martínez-Sansigre, A., Rawlings, S., Lacy, M. et al. The obscuration by dust of most of the growth of supermassive black holes. Nature 436, 666–669 (2005).

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