Large scale structures around radio galaxies at z~1.5
  We explore the environments of two radio galaxies at z~1.5, 7C1751+6809 and
7C1756+6520, using deep optical and near-infrared imaging. Our data cover
15'x15' 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 7C1751+6809. In
contrast, 7C1756+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
7C1756+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 (r<2Mpc) 7C1756+6520, and find a clear red sequence that is
truncated at Ks~21.5 (AB). We also find an overdensity of mid-IR selected AGN
in the surroundings of 7C1756+6520. These results are suggestive of a
proto-cluster at high redshift.
