Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Central powering of the largest Lyman-α nebula is revealed by polarized radiation


High-redshift Lyman-α (Lyα) blobs1,2 are extended, luminous but rare structures that seem to be associated with the highest peaks in the matter density of the Universe3,4,5,6. Their energy output and morphology are similar to those of powerful radio galaxies7, but the source of the luminosity is unclear. Some blobs are associated with ultraviolet or infrared bright galaxies, suggesting an extreme starburst event or accretion onto a central black hole8,9,10. Another possibility is gas that is shock-excited by supernovae11,12. But not all blobs are associated with galaxies13,14, and these ones may instead be heated by gas falling into a dark-matter halo15,16,17,18,19. The polarization of the Lyα emission can in principle distinguish between these options20,21,22, but a previous attempt to detect this signature returned a null detection23. Here we report observations of polarized Lyα from the blob LAB1 (ref. 2). Although the central region shows no measurable polarization, the polarized fraction (P) increases to 20 per cent at a radius of 45 kiloparsecs, forming an almost complete polarized ring. The detection of polarized radiation is inconsistent with the in situ production of Lyα photons, and we conclude that they must have been produced in the galaxies hosted within the nebula, and re-scattered by neutral hydrogen.

This is a preview of subscription content, access via your institution

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: LAB1 in Lyα.
Figure 2: The polarization of LAB1.
Figure 3: The radial polarization profile.


  1. Francis, P. J. et al. A group of galaxies at redshift 2.38. Astrophys. J. 457, 490–499 (1996)

    Article  ADS  CAS  Google Scholar 

  2. Steidel, C. C. et al. Lyα imaging of a proto-cluster region at <z> = 3.09. Astrophys. J. 532, 170–182 (2000)

    Article  ADS  Google Scholar 

  3. Palunas, P., Teplitz, H. I., Francis, P. J., Williger, G. M. & Woodgate, B. E. The distribution of Lyα-emitting galaxies at z = 2.38. Astrophys. J. 602, 545–554 (2004)

    Article  ADS  Google Scholar 

  4. Matsuda, Y. et al. A Subaru search for Lyα blobs in and around the protocluster region at redshift z = 3.1. Astron. J. 128, 569–584 (2004)

    Article  ADS  CAS  Google Scholar 

  5. Yang, Y., Zabludoff, A., Tremonti, C., Eisenstein, D. & Davé, R. Extended Lyα nebulae at z ≈ 2.3: an extremely rare and strongly clustered population? Astrophys. J. 693, 1579–1587 (2009)

    Article  ADS  CAS  Google Scholar 

  6. Prescott, M. K. M., Kashikawa, N., Dey, A. & Matsuda, Y. The overdense environment of a large Lyα nebula at z 2.7. Astrophys. J. 678, L77–L80 (2008)

    Article  ADS  CAS  Google Scholar 

  7. Saito, T. et al. Systematic survey of extended Lyα sources over z 3–5. Astrophys. J. 648, 54–66 (2006)

    Article  ADS  CAS  Google Scholar 

  8. Geach, J. E. et al. The Chandra Deep Protocluster Survey: Lyα blobs are powered by heating, not cooling. Astrophys. J. 700, 1–9 (2009)

    Article  ADS  CAS  Google Scholar 

  9. Scarlata, C. et al. He ii emission in Lyα nebulae: active galactic nucleus or cooling radiation? Astrophys. J. 706, 1241–1252 (2009)

    Article  ADS  CAS  Google Scholar 

  10. Colbert, J. W. et al. Polycyclic aromatic hydrocarbon emission within Lyα blobs. Astrophys. J. 728, 59–71 (2011)

    Article  ADS  Google Scholar 

  11. Taniguchi, Y. & Shioya, Y. Superwind model of extended Lyα emitters at high redshift. Astrophys. J. 532, L13–L16 (2000)

    Article  ADS  CAS  Google Scholar 

  12. Mori, M., Umemura, M. & Ferrara, A. The nature of Lyα blobs: supernova-dominated primordial galaxies. Astrophys. J. 613, L97–L100 (2004)

    Article  ADS  CAS  Google Scholar 

  13. Nilsson, K. K., Fynbo, J. P. U., Møller, P., Sommer-Larsen, J. & Ledoux, C. A. Lyman-α blob in the GOODS South field: evidence for cold accretion onto a dark matter halo. Astron. Astrophys. 452, L23–L26 (2006)

    Article  ADS  Google Scholar 

  14. Smith, D. J. B. & Jarvis, M. J. Evidence for cold accretion onto a massive galaxy at high redshift? Mon. Not. R. Astron. Soc. 378, L49–L53 (2007)

    Article  ADS  Google Scholar 

  15. Fardal, M. A. et al. Cooling radiation and the Lyα luminosity of forming galaxies. Astrophys. J. 562, 605–617 (2001)

    Article  ADS  CAS  Google Scholar 

  16. Yang, Y. et al. Probing galaxy formation with He ii cooling lines. Astrophys. J. 640, 539–552 (2006)

    Article  ADS  CAS  Google Scholar 

  17. Dijkstra, M. & Loeb, A. Lyα blobs as an observational signature of cold accretion streams into galaxies. Mon. Not. R. Astron. Soc. 400, 1109–1120 (2009)

    Article  ADS  CAS  Google Scholar 

  18. Goerdt, T. et al. Gravity-driven Lyα blobs from cold streams into galaxies. Mon. Not. R. Astron. Soc. 407, 613–631 (2010)

    Article  ADS  CAS  Google Scholar 

  19. Faucher-Giguère, C.-A., Keresˇ, D., Dijkstra, M., Hernquist, L. & Zaldarriaga, M. Lyα cooling emission from galaxy formation. Astrophys. J. 725, 633–657 (2010)

    Article  ADS  Google Scholar 

  20. Lee, H. & Ahn, S. Polarization of the Ly α from an anisotrophy expanding H i shell in primeval galaxies. Astrophys. J. 504, L61–L64 (1998)

    Article  ADS  CAS  Google Scholar 

  21. Dijkstra, M. & Loeb, A. The polarization of scattered Lyα radiation around high-redshift galaxies. Mon. Not. R. Astron. Soc. 386, 492–504 (2008)

    Article  ADS  Google Scholar 

  22. Rybicki, G. B. & Loeb, A. Polarization of the Lyα halos around sources before cosmological reionization. Astrophys. J. 520, L79–L81 (1999)

    Article  ADS  CAS  Google Scholar 

  23. Prescott, M. K. M., Smith, P. S., Schmidt, G. D. & Dey, A. The line polarization within a giant Lyα nebula. Astrophys. J. 730, L25–L30 (2011)

    Article  ADS  Google Scholar 

  24. Stenflo, J. O. Resonance-line polarization. V. Quantum-mechanical interference between states of different total angular momentum. Astron. Astrophys. 84, 68–74 (1980)

    ADS  CAS  Google Scholar 

  25. Adams, T. F. The escape of resonance-line radiation from extremely opaque media. Astrophys. J. 174, 439–448 (1972)

    Article  ADS  Google Scholar 

  26. Neufeld, D. A. The transfer of resonance-line radiation in static astrophysical media. Astrophys. J. 350, 216–241 (1990)

    Article  ADS  CAS  Google Scholar 

  27. Kereš, D., Katz, N., Weinberg, D. H. & Davé, R. How do galaxies get their gas? Mon. Not. R. Astron. Soc. 363, 2–28 (2005)

    Article  ADS  Google Scholar 

  28. Dekel, A. & Birnboim, Y. Gravitational quenching in massive galaxies and clusters by clumpy accretion. Mon. Not. R. Astron. Soc. 383, 119–138 (2008)

    Article  ADS  CAS  Google Scholar 

  29. Wardle, J. F. C. & Kronberg, P. P. The linear polarization of quasi-stellar radio sources at 3.71 and 11.1 centimeters. Astrophys. J. 194, 249–255 (1974)

    Article  ADS  Google Scholar 

Download references


We thank P. Ogle and J. Colbert for valuable suggestions about polarimetric observations; N. Panagia and T. Jones for comments on the manuscript; and D. Schaerer, N. Scoville, C. Lidman, A. Dey, M. Prescott and P. Lynam for discussions. This work was based on observations made with European Southern Observatory telescopes at the Paranal Observatory under programme ID 084.A-0954. M.H. was supported in part by the Swiss National Science Foundation, and also received support from Agence Nationale de la Recherche (reference ANR-09-BLAN-0234-01).

Author information

Authors and Affiliations



All authors contributed to the proposal preparation. M.H. and C.S. observed and reduced the data. M.H. analysed the results. All authors contributed to the manuscript preparation.

Corresponding author

Correspondence to Matthew Hayes.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

The file contains Supplementary Text and Data 1-6, Supplementary Figures 1-3 with legends and additional references. (PDF 349 kb)

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Hayes, M., Scarlata, C. & Siana, B. Central powering of the largest Lyman-α nebula is revealed by polarized radiation. Nature 476, 304–307 (2011).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing