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Published November 2009 | Published
Journal Article Open

Large scale structures around radio galaxies at z ~ 1.5


We explore the environments of two radio galaxies at z ~ 1.5, 7C 1751+6809 and 7C 1756+6520, using deep optical and near-infrared imaging. Our data cover 15 × 15 arcmin^2 fields around the radio galaxies. We develop and apply BzK color criteria to select cluster member candidates around the radio galaxies and find no evidence of an overdensity of red galaxies within 2Mpc of 7C 1751+6809. In contrast, 7C 1756+6520 shows a significant overdensity of red galaxies within 2Mpc of the radio galaxy, by a factor of 3.1±0.8 relative to the four MUSYC fields. At small separation (r < 6"), this radio galaxy also has one z > 1.4 evolved galaxy candidate, one z > 1.4 star-forming galaxy candidate, and an AGN candidate (at indeterminate redshift). This is suggestive of several close-by companions. Several concentrations of red galaxies are also noticed in the full 7C 1756+6520 field, forming a possible large-scale structure of evolved galaxies with a NW-SE orientation. We construct the color-magnitude diagram of red galaxies found near 7C 1756+6520 (r < 2 Mpc), and find a clear red sequence that is truncated at K_s ~ 21.5 (AB). We also find an overdensity of mid-infrared selected AGN in the surroundings of 7C 1756+6520. These results are suggestive of a proto-cluster at high redshift.

Additional Information

© ESO 2009. Received 25 March 2009. Accepted 27 August 2009. We are very grateful to S. Adam Stanford for useful discussions and Tadayuki Kodama for having provided the models of red sequences presented in this paper. We thank Brigitte Rocca-Volmerange for her support of this project. We would also like to thank Andrea Grazian (and the GOODSMUSIC team) and Ryan Quadri (and theMUSYC survey team) for useful emails exchanges on their online catalogs. This work is based in part on data products produced at the TERAPIX data center located at the Institut d'Astrophysique de Paris and generated from observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. It is also based on observations obtained at the Hale 200 inch telescope at Palomar Observatory and on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.

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October 19, 2023