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arXiv · 1008.1094

Galaxy protocluster candidates at 1.6<z<2

Audrey Galametz·Joel Vernet·Carlos De Breuck·Nina Hatch·George Miley·Tadayuki Kodama·Jaron Kurk·Roderik Overzier·Alessandro Rettura·Huub Rottgering·Nick Seymour·Bram Venemans·Andrew Zirm
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Abstract

We present a study of protoclusters associated with high redshift radio galaxies. We imaged MRC1017-220 (z=1.77) and MRC0156-252 (z=2.02) using the near-infrared wide-field (7.5'x7.5') imager VLT/HAWK-I in the Y, H and Ks bands. We present the first deep Y-band galaxy number counts within a large area (200 arcmin2). We then develop a purely near-infrared colour selection technique to isolate galaxies at 1.6<z<3 that may be associated with the two targets, dividing them into (i) red passively evolving or dusty star-forming galaxies or (ii) blue/star-formation dominated galaxies with little or no dust. Both targeted fields show an excess of star-forming galaxies with respect to control fields. No clear overdensity of red galaxies is detected in the surroundings of MRC1017-220 although the spatial distribution of the red galaxies resembles a filament-like structure within which the radio galaxy is embedded. In contrast, a significant overdensity of red galaxies is detected in the field of MRC0156-252, ranging from a factor of 2-3 times the field density at large scales (2.5Mpc, angular distance) up to a factor of 3-4 times the field density within a 1Mpc radius of the radio galaxy. Half of these red galaxies have colours consistent with red sequence models at z~2, with a large fraction being bright (Ks<21.5, i.e. massive). In addition, we also find a small group of galaxies within 5" of MRC0156-252 suggesting that the radio galaxy has multiple companions within ~50 kpc. We conclude that the field of MRC0156-252 shows many remarkable similarities with the well-studied protocluster surrounding PKS1138-262 (z=2.16) suggesting that MRC0156-252 is associated with a galaxy protocluster at z~2.

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Audrey Galametz, Joel Vernet, Carlos De Breuck, Nina Hatch, George Miley, Tadayuki Kodama, Jaron Kurk, Roderik Overzier, Alessandro Rettura, Huub Rottgering, Nick Seymour, Bram Venemans, Andrew Zirm. 2010-08-05. Galaxy protocluster candidates at 1.6<z<2. https://doi.org/10.1051/0004-6361/201015035

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