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.

A distortion of very-high-redshift galaxy number counts by gravitational lensing


The observed number counts of high-redshift galaxy candidates1,2,3,4,5,6,7,8 have been used to build up a statistical description of star-forming activity at redshift z 7, when galaxies reionized the Universe1,2,9,10. Standard models11 predict that a high incidence of gravitational lensing will probably distort measurements of flux and number of these earliest galaxies. The raw probability of this happening has been estimated to be 0.5 per cent (refs 11, 12), but can be larger owing to observational biases. Here we report that gravitational lensing is likely to dominate the observed properties of galaxies with redshifts of z 12, when the instrumental limiting magnitude is expected to be brighter than the characteristic magnitude of the galaxy sample. The number counts could be modified by an order of magnitude, with most galaxies being part of multiply imaged systems, located less than 1 arcsec from brighter foreground galaxies at z ≈ 2. This lens-induced association of high-redshift and foreground galaxies has perhaps already been observed among a sample of galaxy candidates identified at z ≈ 10.6. Future surveys will need to be designed to account for a significant gravitational lensing bias in high-redshift galaxy samples.

Your institute does not have access to this article

Relevant articles

Open Access articles citing this article.

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Gravitational lens fractions among candidate high-redshift HUDF galaxies.
Figure 2: Probabilities of multiple imaging of high-redshift galaxies with JWST.
Figure 3: Gravitational-lens-induced modification of the bright end of the high-redshift galaxy luminosity function to be observed with JWST.


  1. Bouwens, R. J. et al. UV luminosity functions from 113 z 7 and z 8 Lyman-break galaxies in the ultra-deep HUDF09 and wide-area ERS WFC3/IR observations. Preprint at 〈〉 (2010)

  2. Lorenzoni, S. et al. Candidate z 8 – 9 galaxies from WFC3 imaging. Preprint at 〈〉 (2010)

  3. Bouwens, R. J. et al. Constraints on the first galaxies: z 10 galaxy candidates from HST WFC3/IR. Preprint at 〈〉 (2009)

  4. Yan, H. et al. Galaxy formation in the reionization epoch as hinted by Wide Field Camera 3 observations of the Hubble Ultra Deep Field. Res. Astron. Astrophys. 10, 867–904 (2010)

    ADS  CAS  Article  Google Scholar 

  5. Bouwens, R. J. et al. Star formation at z 6: the Hubble Ultra Deep Parallel Fields. Astrophys. J. 606, L25–L28 (2004)

    ADS  CAS  Article  Google Scholar 

  6. Yan, H. & Windhorst, R. A. Candidates of z 5.5 – 7 galaxies in the Hubble Space Telescope Ultra Deep Field. Astrophys. J. 612, L93–L96 (2004)

    ADS  CAS  Article  Google Scholar 

  7. Wilkins, S. M. et al. Probing L * Lyman-break galaxies at z 7 in GOODS-South with WFC3 on Hubble Space Telescope. Mon. Not. R. Astron. Soc. 403, 938–944 (2010)

    ADS  Article  Google Scholar 

  8. McLure, R. J. et al. Galaxies at z = 6 – 9 from the WFC3/IR imaging of the Hubble Ultra Deep Field. Mon. Not. R. Astron. Soc. 403, 960–983 (2010)

    ADS  Article  Google Scholar 

  9. Yan, H. & Windhorst, R. A. The major sources of the cosmic reionizing background at z 6. Astrophys. J. 600, L1–L5 (2004)

    ADS  CAS  Article  Google Scholar 

  10. Trenti, M. et al. The galaxy luminosity function during the reionization epoch. Astrophys. J. 714, L202–L207 (2010)

    ADS  CAS  Article  Google Scholar 

  11. Barkana, R. & Loeb, A. High-redshift galaxies: their predicted size and surface brightness distributions and their gravitational lensing probability. Astrophys. J. 531, 613–623 (2000)

    ADS  Article  Google Scholar 

  12. Comerford, J. M., Haiman, Z. & Schaye, J. Constraining the redshift z 6 quasar luminosity function using gravitational lensing. Astrophys. J. 580, 63–72 (2002)

    ADS  Article  Google Scholar 

  13. Turner, E. L., Ostriker, J. P. & Gott, J. R., III The statistics of gravitational lenses — the distributions of image angular separations and lens redshifts. Astrophys. J. 284, 1–22 (1984)

    ADS  Article  Google Scholar 

  14. Richard, J. et al. A Hubble and Spitzer Space Telescope survey for gravitationally lensed galaxies: further evidence for a significant population of low-luminosity galaxies beyond z = 7. Astrophys. J. 685, 705–724 (2008)

    ADS  CAS  Article  Google Scholar 

  15. Bradley, L. D. et al. Discovery of a very bright strongly lensed galaxy candidate at z 7.6. Astrophys. J. 678, 647–654 (2008)

    ADS  CAS  Article  Google Scholar 

  16. Zheng, W. et al. Bright strongly lensed galaxies at redshift z 6 – 7 behind the clusters Abell 1703 and CL0024+16. Astrophys. J. 697, 1907–1917 (2009)

    ADS  Article  Google Scholar 

  17. Bouwens, R. J. et al. z 7 – 10 galaxies behind lensing clusters: contrast with field search results. Astrophys. J. 690, 1764–1771 (2009)

    ADS  CAS  Article  Google Scholar 

  18. Webster, R. L., Hewett, P. C., Harding, M. E. & Wegner, G. A. Detection of statistical gravitational lensing by foreground mass distributions. Nature 336, 358–359 (1988)

    ADS  Article  Google Scholar 

  19. Nollenberg, J. G. & Williams, L. L. R. Galaxy-quasar correlations between APM galaxies and Hamburg-ESO QSOs. Astrophys. J. 634, 793–805 (2005)

    ADS  CAS  Article  Google Scholar 

  20. Scranton, R. et al. Detection of cosmic magnification with the Sloan Digital Sky Survey. Astrophys. J. 633, 589–602 (2005)

    ADS  CAS  Article  Google Scholar 

  21. Windhorst, R. A., Cohen, S. H., Jansen, R. A., Conselice, C. & Yan, H. How JWST can measure first light, reionization and galaxy assembly. N. Astron. Rev. 50, 113–120 (2006)

    ADS  Article  Google Scholar 

  22. Schechter, P. An analytic expression for the luminosity function for galaxies. Astrophys. J. 203, 297–306 (1976)

    ADS  Article  Google Scholar 

  23. Pei, Y. C. Magnification of quasars by cosmologically distributed gravitational lenses. Astrophys. J. 440, 485–500 (1995)

    ADS  Article  Google Scholar 

  24. Greif, T. H., Johnson, J. L., Bromm, V. & Klessen, R. S. The first supernova explosions: energetics, feedback, and chemical enrichment. Astrophys. J. 670, 1–14 (2007)

    ADS  CAS  Article  Google Scholar 

  25. Hathi, N. P. et al. UV-dropout galaxies in the GOODS-South Field from WFC3 early release science observations. Astrophys. J. 720, 1708–1716 (2010)

    ADS  CAS  Article  Google Scholar 

  26. Oguri, M. et al. The Sloan Digital Sky Survey quasar lens search. III. Constraints on dark energy from the third data release quasar lens catalog. Astron. J. 135, 512–519 (2008)

    ADS  Article  Google Scholar 

  27. Choi, Y., Park, C. & Vogeley, M. S. Internal and collective properties of galaxies in the Sloan Digital Sky Survey. Astrophys. J. 658, 884–897 (2007)

    ADS  Article  Google Scholar 

  28. Huterer, D., Keeton, C. R. & Ma, C. Effects of ellipticity and shear on gravitational lens statistics. Astrophys. J. 624, 34–45 (2005)

    ADS  Article  Google Scholar 

  29. Komatsu, E. et al. Five-year Wilkinson Microwave Anisotropy Probe observations: cosmological interpretation. Astrophys. J. Suppl. 180330–376 (2009)

  30. Windhorst, R. A. et al. High resolution science with high redshift galaxies. Adv. Space Res. 41, 1965–1971 (2008)

    ADS  Article  Google Scholar 

Download references


We thank K.-H. Chae for discussing results of his lensing calculations. J.S.B.W. was supported in part by a QE-II fellowship and grants from the Australian Research Council. H.Y. acknowledges support from the long-term fellow-ship programme of the Center for Cosmology and AstroParticle Physics (CCAPP) at The Ohio State University. H.Y. and R.A.W. were supported by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. R.A.W. was supported by a NASA JWST Interdisciplinary Scientist grant.

Author information

Authors and Affiliations



J.S.B.W. performed the calculations of lensing probabilities. H.Y. measured the distributions of galaxy properties from the HUDF. All authors were involved in the conception of the work, discussing the results, and writing the manuscript.

Corresponding author

Correspondence to J. Stuart B. Wyithe.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

The file contains Supplementary Text, Supplementary References and Supplementary Figures 1-5 with legends. (PDF 621 kb)

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Wyithe, J., Yan, H., Windhorst, R. et al. A distortion of very-high-redshift galaxy number counts by gravitational lensing. Nature 469, 181–184 (2011).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

Further reading


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