Three candidate clusters around high Redshift radio-loud sources: MG1 J04426+0202, 3C 068.2, and MS 1426.9+1052

We present near-infrared observations of the environments around three radio-loud sources (MG1 J0442+0202, 3C 068.2, and MS $1426.9+1052$) at redshifts z = 1.10, 1.57, and 1.83 (respectively) that are surrounded by near-infrared galaxy overdensities. Overdensities with respect to field counts were found to be significant up to 19σ, with 12 times the expected number of galaxies within the inner regions of the densest proto-cluster. Color–magnitude relations are constructed in K_s, J − K_s, with each candidate cluster exhibiting a feature consistent with the beginnings of a red sequence (RS). Galaxy models based on the redshift of the radio source are used to compare expected CMRs for a given formation epoch with the observed RS of each candidate, and are found to be consistent with an old ($z_f>5$) formation epoch for a few bright, red galaxies on the RS.