Volume 483, Number 3, June I 2008
|Page(s)||L39 - L42|
|Published online||16 April 2008|
Letter to the Editor
GMASS ultradeep spectroscopy of galaxies at z
III. The emergence of the color bimodality at z
Laboratoire d'Astrophysique de Marseille, OAMP, UMR6110, CNRS-Université de Provence Aix-Marseille I, BP 8, 13376 Marseille Cedex 12, France e-mail: email@example.com
2 Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy
3 Max-Planck-Institut für Astronomie, Königstul 17, 69117 Heidelberg, Germany
4 Dipartimento di Astronomia, Università di Padova, Vicolo dell'Osservatorio 2, 35122 Padova, Italy
5 INAF - Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
6 CEA-Saclay, DSM/DAPNIA/Service d'Astrophysique, 91191 Gif-sur-Yvette Cedex, France
7 Max Planck Institut für Extraterrestrische Physik, Postfach 1312, 85741 Garching bei München, Germany
8 NOAO-Tucson, 950 North Cherry Avenue, Tucson, AZ 85719, USA
9 INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
10 INAF - Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
11 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
Accepted: 8 April 2008
Aims. The aim of this work is to study the evolution of the rest-frame color distribution of galaxies with the redshift, in particular in the critical interval .
Methods. We combined ultradeep spectroscopy from the GMASS project (Galaxy Mass Assembly ultradeep Spectroscopic Survey) with GOODS multi-band photometry (from optical to mid-infrared) to study a sample of 1021 galaxies up to m(4.5 μm) = 23.
Results. We find that the distribution of galaxies in the color vs. stellar mass plane is bimodal up to at least redshift . We define a “mass complete” sample of galaxies residing on the red sequence, selecting objects with , and we study their morphological and spectro-photometric properties. We show that the contribution to this sample of early-type galaxies, defined as galaxies with a spheroidal morphology and no star formation, decreases from 60-70% at 0.5 down to ~50% at redshift . At we still find red galaxies in the mass complete sample, even if the bimodality is not seen any more. About 25% of these red galaxies at are passively evolving, with the bulk of their stars formed at redshift .
Key words: cosmology: observations / galaxies: fundamental parameters / galaxies: evolution / galaxies: formation
© ESO, 2008
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