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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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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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