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

Nature 437, 519-521 (22 September 2005) | doi: 10.1038/nature03979

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

O. Le Fèvre¹, S. Paltani¹, S. Arnouts¹, S. Charlot^2,³, S. Foucaud⁴, O. Ilbert^1,⁵, H. J. McCracken^3,¹², G. Zamorani⁶, D. Bottini⁴, B. Garilli⁴, V. Le Brun¹, D. Maccagni⁴, J. P. Picat⁷, R. Scaramella⁸, M. Scodeggio⁴, L. Tresse¹, G. Vettolani⁸, A. Zanichelli⁸, C. Adami¹, S. Bardelli⁶, M. Bolzonella⁵, A. Cappi⁶, P. Ciliegi⁶, T. Contini⁷, P. Franzetti⁴, I. Gavignaud^7,⁹, L. Guzzo¹⁰, A. Iovino¹⁰, B. Marano⁵, C. Marinoni¹⁰, A. Mazure¹, B. Meneux¹, R. Merighi⁶, R. Pellò⁷, A. Pollo¹⁰, L. Pozzetti⁶, M. Radovich¹¹, E. Zucca⁶, M. Arnaboldi¹¹, M. Bondi⁸, A. Bongiorno⁵, G. Busarello¹¹, L. Gregorini⁸, F. Lamareille⁷, G. Mathez⁷, Y. Mellier^3,¹², P. Merluzzi¹¹, V. Ripepi¹¹ and D. Rizzo⁷

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 colours^2,^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 estimates^2,^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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Laboratoire d'Astrophysique de Marseille, OAMP, UMR6110, CNRS, Université de Provence Aix-Marseille I, BP8, F-13376 Marseille cedex 12, France
Max Planck Institut fur Astrophysik, D-85741 Garching, Germany
Institut d'Astrophysique de Paris, UMR 7095, 98 bis Bvd Arago, F-75014 Paris, France
IASF-INAF, via Bassini 15, I-20133, Milano, Italy
Università di Bologna, Dipartimento di Astronomia, via Ranzani 1, I-40127, Bologna, Italy
INAF, Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127, Bologna, Italy
Laboratoire d'Astrophysique de l'Observatoire Midi-Pyrénées (UMR 5572), 14 avenue E. Belin, F-31400 Toulouse, France
IRA-INAF, via Gobetti 101, I-40129, Bologna, Italy
European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching, Germany
INAF, Osservatorio Astronomico di Brera, via Brera 28, Milan, Italy
INAF, Osservatorio Astronomico di Capodimonte, via Moiariello 16, I-80131, Napoli, Italy
Observatoire de Paris, LERMA, 61 Avenue de l'Observatoire, F-75014 Paris, France

Correspondence to: O. Le Fèvre¹ Correspondence and requests for materials should be addressed to O.L.F. (Email: Olivier.LeFevre@oamp.fr).

Received 26 April 2005; Accepted 29 June 2005

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