Volume 576, April 2015
|Number of page(s)||5|
|Published online||23 March 2015|
Passive galaxies as tracers of cluster environments at z ~ 2
1 Irfu/Service d’Astrophysique, CEA Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette, France
2 Department of Physics, Ludwig-Maximilians-Universität, Scheinerstr. 1, 81679 München, Germany
3 INAF−IASF, via Bassini 15, 20133 Milano, Italy
4 INAF−Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
5 Institute for Astronomy, ETH Zürich, Wolfgang-Pauli-strasse 27, 8093 Zürich, Switzerland
6 INAF-Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
7 Dipartimento di Fisica e Astronomia, Universitá di Bologna, Viale Berti Pichat 6/2, 30127 Bologna, Italy
8 Department of Physics, University of Helsinki, Gustaf Hällströmin katu 2a, 0014 Helsinki, Finland
9 National Astronomical Observatory of Japan, Subaru Telescope, 650 North Aohoku Place, Hilo, HI 96720, USA
10 Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford, OX1 3RH, UK
11 IRAM−Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 Saint-Martin dHères, France
12 Institut dAstrophysique de Paris, UMR 7095 CNRS, Université Pierre et Marie Curie, 75005 Paris, France
Received: 22 September 2014
Accepted: 17 January 2015
Even 10 billion years ago, the cores of the first galaxy clusters are often found to host a characteristic population of massive galaxies with already suppressed star formation. Here we search for distant cluster candidates at z ~ 2 using massive passive galaxies as tracers. With a sample of ~40 spectroscopically confirmed passive galaxies at 1.3 < z < 2.1, we tuned photometric redshifts of several thousand passive sources in the 2 sq. deg COSMOS field. This allowed us to map their density in redshift slices, probing the large-scale structure in the COSMOS field as traced by passive sources. We report here on the three strongest passive galaxy overdensities that we identify in the range 1.5 < z < 2.5. While the actual nature of these concentrations still needs to be confirmed, we discuss their identification procedure and the arguments supporting them as candidate galaxy clusters (probably in the mid-1013 M⊙ range). Although this search approach is probably biased toward more evolved structures, it has the potential of selecting still rare, cluster-like environments close to their epoch of first appearance, enabling new investigations of the evolution of galaxies in the context of structure growth.
Key words: galaxies: clusters: general / galaxies: high-redshift / large-scale structure of Universe
© ESO, 2015
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