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A galaxy at a redshift z = 6.96


When galaxy formation started in the history of the Universe remains unclear. Studies of the cosmic microwave background indicate that the Universe, after initial cooling (following the Big Bang), was reheated and reionized by hot stars in newborn galaxies at a redshift in the range 6 < z < 14 (ref. 1). Though several candidate galaxies at redshift z > 7 have been identified photometrically2,3, galaxies with spectroscopically confirmed redshifts have been confined to z < 6.6 (refs 4–8). Here we report a spectroscopic redshift of z = 6.96 (corresponding to just 750 Myr after the Big Bang) for a galaxy whose spectrum clearly shows Lyman-α emission at 9,682 Å, indicating active star formation at a rate of 10M yr-1, where M is the mass of the Sun. This demonstrates that galaxy formation was under way when the Universe was only 6 per cent of its present age. The number density of galaxies at z ≈ 7 seems to be only 18–36 per cent of the density at z = 6.6.

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Figure 1: Multi-waveband 20″ × 20″ images of the z = 6.96 Lyman α emitter IOK-1 and the unidentified candidate IOK-2.
Figure 2: Combined spectrum of z = 6.96 galaxy, IOK-1.
Figure 3: Decline of the number density of LAEs between 6.6 < z < 7.0.

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  1. Page, L. et al. Three year Wilkinson Microwave Anisotropy Probe (WMAP) observations: polarization analysis. Astrophys. J. (submitted); preprint at (2006)

  2. Egami, E. et al. Spitzer and Hubble Space Telescope constraints on the physical properties of the z7 galaxy strongly lensed by A2218. Astrophys. J. 618, L5–L8 (2005)

    Article  ADS  Google Scholar 

  3. Bouwens, R. J. et al. Constraints on z ≈ 10 galaxies from the deepest Hubble Space Telescope NICMOS fields. Astrophys. J. 624, L5–L8 (2005)

    Article  ADS  CAS  Google Scholar 

  4. Hu, E. M., McMahon, R. G. & Cowie, L. L. An extremely luminous galaxy at z = 5.74. Astrophys. J. 521, L9–L12 (1999)

    Article  ADS  Google Scholar 

  5. Hu, E. M. et al. A redshift z = 6.56 galaxy behind the cluster Abell 370. Astrophys. J. 568, L75–L79 (2002)

    Article  ADS  CAS  Google Scholar 

  6. Ajiki, M. et al. A Subaru search for Ly α emitters at redshift 5.7. Astron. J. 126, 2091–2107 (2003)

    Article  ADS  CAS  Google Scholar 

  7. Taniguchi, Y. et al. The SUBARU Deep Field Project: Lyman α emitters at a redshift of 6.6. Publ. Astron. Soc. Jpn 57, 165–182 (2005)

    Article  ADS  CAS  Google Scholar 

  8. Kashikawa, N. et al. The Subaru Deep Field: The optical imaging data. Publ. Astron. Soc. Jpn 56, 1011–1023 (2004)

    Article  ADS  Google Scholar 

  9. Stark, D. P. & Ellis, R. S. Searching for the sources responsible for cosmic reionisation: probing the redshift range 7 &lt; z &lt; 10 and beyond. New Astron. Rev. 50, 46–52 (2006)

    Article  ADS  Google Scholar 

  10. Willis, J. P. & Courbin, F. A deep, narrow J-band search for protogalactic Ly-α emission at redshift z9. Mon. Not. R. Astron. Soc. 357, 1348–1356 (2005)

    Article  ADS  CAS  Google Scholar 

  11. Barton, E. J., Bullock, J. S., Cooray, A. & Kaplinghat, M. First light and reionisation: a conference summary. New Astron. Rev. 50, 1–12 (2006)

    Article  ADS  Google Scholar 

  12. Horton, A. et al. DAzLE: The Dark Ages z (redshift) Lyman-α explorer. Proc. SPIE 5492, 1022–1032 (2004)

    Article  ADS  Google Scholar 

  13. Iye, M. et al. Current performance and on-going improvements of the 8.2 m Subaru Telescope. Publ. Astron. Soc. Jpn 56, 381–397 (2004)

    Article  ADS  Google Scholar 

  14. Miyazaki, S. et al. Subaru Prime Focus Camera—Suprime-Cam. Publ. Astron. Soc. Jpn 54, 833–853 (2002)

    Article  ADS  Google Scholar 

  15. Bruzual, G. & Charlot, S. Stellar population synthesis at the resolution of 2003. Mon. Not. R. Astron. Soc. 344, 1000–1028 (2003)

    Article  ADS  Google Scholar 

  16. Madau, P. Radiative transfer in a clumpy Universe: the colors of high-redshift galaxies. Astrophys. J. 441, 18–27 (1995)

    Article  ADS  Google Scholar 

  17. Kashikawa, N. et al. FOCAS: The Faint Object Camera and Spectrograph for the Subaru Telescope. Publ. Astron. Soc. Jpn 54, 819–832 (2002)

    Article  ADS  Google Scholar 

  18. Hu, E. M. et al. The luminosity function of Ly-α emitters at redshift z5.7. Astron. J. 127, 563–575 (2004)

    Article  ADS  Google Scholar 

  19. Sheth, R. K. & Tormen, C. Large-scale bias and the peak background split. Mon. Not. R. Astron. Soc. 308, 119–126 (1999)

    Article  ADS  CAS  Google Scholar 

  20. Ouchi, M. et al. The discovery of primeval large-scale structures with forming clusters at redshift 6. Astrophys. J. 620, L1–L4 (2005)

    Article  ADS  Google Scholar 

  21. Gehrels, N. Confidence limits for small numbers of events in astrophysical data. Astrophys. J. 303, 336–346 (1986)

    Article  ADS  CAS  Google Scholar 

  22. Kashikawa, N. et al. The end of the reionisation epoch probed by Lyman α emitters at z = 6.5 in the Subaru Deep Field. Astrophys. J. 648 (in the press); preprint at (2006)

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

    Article  ADS  CAS  Google Scholar 

  24. Gunn, J. E. & Peterson, B. A. On the density of neutral hydrogen in intergalactic space. Astrophys. J. 142, 1633–1641 (1965)

    Article  ADS  CAS  Google Scholar 

  25. Fan, X. et al. Evolution of the ionizing background and the epoch of reionisation from the spectra of z6 quasars. Astron. J. 123, 1247–1257 (2002)

    Article  ADS  Google Scholar 

  26. Malhotra, S. & Rhoads, J. E. Luminosity functions of Ly α emitters at redshifts z = 6.5 and z = 5.7: evidence against reionisation at z6.5. Astrophys. J. 617, L5–L8 (2004)

    Article  ADS  CAS  Google Scholar 

  27. Kennicutt, R. C. J. Star formation in galaxies along the Hubble sequence. Annu. Rev. Astron. Astrophys. 36, 189–232 (1998)

    Article  ADS  CAS  Google Scholar 

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This work is based on data collected with the Subaru Telescope, operated by the National Astronomical Observatory of Japan and was partly supported by KAKENHI. We thank the SDF team and the staff at the Subaru Observatory for providing the data and assisting us with observations and data reduction. K.O. acknowledges a fellowship from the Japan Society for the Promotion of Science. Author Contributions M.I., the principal investigator, proposed this project, designed the NB973 filter and led the observations. K.O. made all the observations, including the slit mask design for the spectroscopy, carried out all the data reduction and analysis and produced the figures. M.I. and K.O. jointly wrote the paper. N.K. contributed to observations, data analysis and discussion. H.F. and Takashi. H. helped with the Suprime-Cam imaging and FOCAS spectroscopy, respectively, as instrument support astronomers. K.S. and M.O. commented on the manuscript. T.M. investigated the possibility of the unconfirmed candidate being a variable object. Y.M., K.O. and Tetsuya H. measured the transmission curve of the NB973 filter.

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Correspondence to Masanori Iye.

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Iye, M., Ota, K., Kashikawa, N. et al. A galaxy at a redshift z = 6.96. Nature 443, 186–188 (2006).

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