Escape of about five per cent of Lyman-α photons from high-redshift star-forming galaxies

Article metrics

Abstract

The Lyman-α (Lyα) emission line is the primary observational signature of star-forming galaxies at the highest redshifts1, and has enabled the compilation of large samples of galaxies with which to study cosmic evolution2,3,4,5. The resonant nature of the line, however, means that Lyα photons scatter in the neutral interstellar medium of their host galaxies, and their sensitivity to absorption by interstellar dust may therefore be greatly enhanced. This implies that the Lyα luminosity may be significantly reduced, or even completely suppressed. Hitherto, no unbiased empirical test of the escaping fraction (fesc) of Lyα photons has been performed at high redshifts. Here we report that the average fesc from star-forming galaxies at redshift z = 2.2 is just 5 per cent by performing a blind narrowband survey in Lyα and Hα. This implies that numerous conclusions based on Lyα-selected samples will require upwards revision by an order of magnitude and we provide a benchmark for this revision. We demonstrate that almost 90 per cent of star-forming galaxies emit insufficient Lyα to be detected by standard selection criteria2,3,4,5. Both samples show an anti-correlation of fesc with dust content, and we show that Lyα- and Hα-selection recovers populations that differ substantially in dust content and fesc.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Figure 1: Observed Hα and Lyα luminosities.
Figure 2: Lyα luminosity functions.
Figure 3: Escape fraction ( fesc) and dust attenuation ( EB-V ).

References

  1. 1

    Partridge, R. B. & Peebles, P. J. E. Are young galaxies visible? Astrophys. J. 147, 868–886 (1967)

  2. 2

    Hu, E. M., Cowie, L. L. & McMahon, R. G. The density of Lyα emitters at very high redshift. Astrophys. J. 502, L99–L103 (1998)

  3. 3

    Malhotra, S. & Rhoads, J. E. Large equivalent width Lyα line emission at z = 4.5: young galaxies in a young universe? Astrophys. J. 565, L71–L74 (2002)

  4. 4

    Gronwall, C. et al. Lyα emission-line galaxies at z = 3.1 in the Extended Chandra Deep Field-South. Astrophys. J. 667, 79–91 (2007)

  5. 5

    Ouchi, M. et al. The Subaru/XMM-Newton Deep Survey (SXDS). IV. Evolution of Lyα emitters from z = 3.1 to 5.7 in the 1 deg2 field: luminosity functions and AGN. Astrophys. J. Suppl. Ser. 176, 301–330 (2008)

  6. 6

    Charlot, S. & Fall, S. M. Lyman-alpha emission from galaxies. Astrophys. J. 415, 580–588 (1993)

  7. 7

    Schaerer, D. The transition from Population III to normal galaxies: Lyα and He ii emission and the ionising properties of high redshift starburst galaxies. Astron. Astrophys. 397, 527–538 (2003)

  8. 8

    Östlin, G. et al. The Lyman alpha morphology of local starburst galaxies: release of calibrated images. Astron. J. 138, 923–940 (2009)

  9. 9

    Atek, H. et al. Empirical estimate of Lyα escape fraction in a statistical sample of Lyα emitters. Astron. Astrophys. 506, L1–L4 (2009)

  10. 10

    Kornei, K. et al. The relationship between stellar populations and Lyman α emission in Lyman break galaxies. Astrophys. J. 711, 693–710 (2010)

  11. 11

    Verhamme, A. et al. 3D Lyα radiation transfer. III. Constraints on gas and stellar properties of z 3 Lyman break galaxies (LBG) and implications for high-z LBGs and Lyα emitters. Astron. Astrophys. 491, 89–111 (2009)

  12. 12

    Nilsson, K. K. et al. Evolution in the properties of Lyman-α emitters from redshifts z3 to z2. Astron. Astrophys. 498, 13–23 (2009)

  13. 13

    Kennicutt, R. C. Star formation in galaxies along the Hubble sequence. Annu. Rev. Astron. Astrophys. 36, 189–231 (1998)

  14. 14

    Le Delliou, M., Lacey, C. G., Baugh, C. M. & Morris, S. L. The properties of Lyα emitting galaxies in hierarchical galaxy formation models. Mon. Not. R. Astron. Soc. 365, 712–726 (2006)

  15. 15

    Nagamine, K., Ouchi, M., Springel, V. & Hernquist, L. Lyman-alpha emitters and Lyman-break galaxies at z = 3–6 in cosmological SPH simulations. Preprint at 〈http://arXiv.org/abs/0802.0228〉 (2008)

  16. 16

    Deharveng, J.-M. et al. Lyα-emitting galaxies at 0.2<z0.35 from GALEX spectroscopy. Astrophys. J. 680, 1072–1082 (2008)

  17. 17

    Hayes, M., Schaerer, D. & Östlin, G. The H-alpha luminosity function at redshift 2.2: a new determination using VLT/HAWK-I. Astron. Astrophys. 509, L5–L9 (2010)

  18. 18

    Giavalisco, M. et al. The Great Observatories Origins Deep Survey: initial results from optical and near-infrared imaging. Astrophys. J. 600, L93–L98 (2004)

  19. 19

    Santini, P. et al. Star formation and mass assembly in high redshift galaxies. Astron. Astrophys. 504, 751–767 (2009)

  20. 20

    Brocklehurst, M. Calculations of level populations for the low levels of hydrogenic ions in gaseous nebulae. Mon. Not. R. Astron. Soc. 153, 471–490 (1971)

  21. 21

    Santos, M. R. Probing reionization with Lyman α emission lines. Mon. Not. R. Astron. Soc. 349, 1137–1152 (2004)

  22. 22

    Dijkstra, M., Lidz, A. & Wyithe, J. S. B. The impact of the IGM on high-redshift Lyα emission lines. Mon. Not. R. Astron. Soc. 377, 1175–1186 (2007)

  23. 23

    Hayes, M. & Östlin, G. On the narrowband detection properties of high-redshift Lyman-alpha emitters. Astron. Astrophys. 460, 681–694 (2006)

  24. 24

    Bolzonella, M., Miralles, J.-M. & Pelló, R. Photometric redshifts based on standard SED fitting procedures. Astron. Astrophys. 363, 476–492 (2000)

  25. 25

    Verhamme, A., Schaerer, D. & Maselli, A. Lyα radiation transfer. I. Understanding Lyα line profile morphologies. Astron. Astrophys. 460, 397–413 (2006)

  26. 26

    Calzetti, D. et al. The dust content and opacity of actively star-forming galaxies. Astrophys. J. 533, 682–695 (2000)

  27. 27

    Giavalisco, M., Koratkar, A. & Calzetti, D. Obscuration of Ly alpha photons in star-forming galaxies. Astrophys. J. 466, 831–839 (1996)

  28. 28

    Atek, H., Kunth, D., Hayes, M., Östlin, G. & Mas-Hesse, J. M. On the detectability of Lyα emission in star forming galaxies. The role of dust. Astron. Astrophys. 488, 491–509 (2008)

  29. 29

    Scarlata, C. et al. The effect of dust geometry on the Lyα output of galaxies. Astrophys. J. 704, L98–L102 (2009)

  30. 30

    Isobe, T., Feigelson, E. D. & Nelson, P. I. Statistical methods for astronomical data with upper limits. II – Correlation and regression. Astrophys. J. 306, 490–508 (1986)

Download references

Acknowledgements

This work is based on observations made with ESO telescopes at the Paranal Observatory under programme ID 081.A-0932. The filter used to capture Lyα was financed by the Erik and Märta Holmberg foundation for astronomy and physics. M.H., D.S. and S.d.B. acknowledge the support of the Swiss National Science Foundation. G.Ö. is a Swedish Royal Academy of Sciences research fellow supported by the Knut and Alice Wallenberg foundation, and also acknowledges support from the Swedish research council (VR). J.M.M.-H. is funded by Spanish MICINN grants CSD2006-00070 (CONSOLIDER GTC) and AYA2007-67965. We thank D. Valls-Gabaud, M. Ouchi, and C. Scarlata for discussions.

Author Contributions M.H. and G.Ö. conceived the programme and manufactured the custom filter. M.H. observed, and processed and analysed the data. S.d.B. and D.S. wrote tools for analysis of the SED fitting results. A.V. produced the radiation transfer code with D.S. J.M. contributed to the use and processing of auxiliary data. All authors contributed to the interpretation of the data, the research proposal and manuscript preparation.

Author information

Correspondence to Matthew Hayes.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This Supplementary Information file comprises: Survey redshift matching and the custom bandpass; Observations and data reduction; Photometry, selection, and catalogue assembly; SED fitting, dust extinction, and star-formation rates; Luminosity functions, Monte Carlo simulations, and escape fractions; The radiation transfer models and theoretical Lyα escape fractions, Supplementary Tables 1 and 2, Supplementary References and Supplementary Figures SI1 and SI2 with legends. (PDF 387 kb)

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Hayes, M., Östlin, G., Schaerer, D. et al. Escape of about five per cent of Lyman-α photons from high-redshift star-forming galaxies. Nature 464, 562–565 (2010) doi:10.1038/nature08881

Download citation

Further reading

Comments

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.