An Overdensity of Galaxies near the Most Distant Radio-loud Quasar*

A 5 arcmin2 region around the luminous radio-loud quasar SDSS J0836+0054 (z = 5.8) hosts a wealth of associated galaxies, characterized by very red (1.3 < i775 - z850 < 2.0) color. The surface density of these z ~ 5.8 candidates is approximately 6 times higher than the number expected from deep ACS fields. This is one of the highest galaxy overdensities at high redshifts, which may develop into a group or cluster. We also find evidence for a substructure associated with one of the candidates. It has two very faint companion objects within 2'', which are likely to merge. The finding supports the results of a recent simulation, which finds that luminous quasars at high redshifts lie on the most prominent dark matter filaments and are surrounded by many fainter galaxies. The quasar activity from these regions may signal the buildup of a massive system.