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A large population of galaxies 9 to 12 billion years back in the history of the Universe


To understand the evolution of galaxies, we need to know as accurately as possible how many galaxies were present in the Universe at different epochs1. Galaxies in the young Universe have hitherto mainly been identified using their expected optical colours2,3,4, but this leaves open the possibility that a significant population remains undetected because their colours are the result of a complex mix of stars, gas, dust or active galactic nuclei. Here we report the results of a flux-limited I-band survey of galaxies at look-back times of 9 to 12 billion years. We find 970 galaxies with spectroscopic redshifts between 1.4 and 5. This population is 1.6 to 6.2 times larger than previous estimates2,3,4, with the difference increasing towards brighter magnitudes. Strong ultraviolet continua (in the rest frame of the galaxies) indicate vigorous star formation rates of more than 10–100 solar masses per year. As a consequence, the cosmic star formation rate representing the volume-averaged production of stars is higher than previously measured at redshifts of 3 to 4.

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Figure 1: Average spectra of VVDS galaxies.
Figure 2: Galaxy surface density.
Figure 3: The ( u g, g r ) colour diagram of the VVDS high-redshift galaxies.

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We thank the ESO for continuous support of this programme; the CNRS, the University of Provence and the Italian INAF for funding; and S. J. Lilly and A. Renzini for discussions. The observations reported here are based on observations obtained at the European Southern Observatory Very Large Telescope, and on data products produced at TERAPIX and the Canadian Astronomy Data Centre as part of the Canada-France-Hawaii Telescope Legacy Survey, a collaborative project of NRC and CNRS.

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Correspondence to O. Le Fèvre.

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Le Fèvre, O., Paltani, S., Arnouts, S. et al. A large population of galaxies 9 to 12 billion years back in the history of the Universe. Nature 437, 519–521 (2005).

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