We report the discovery of a remarkable concentration of massive galaxies with extended X-
ray emission at z spec= 2.506, which contains 11 massive (M*≳ 10 11 M⊙) galaxies in the
central 80 kpc region (11.6σ overdensity). We have spectroscopically confirmed 17 member
galaxies with 11 from CO and the remaining ones from Hα. The X-ray luminosity, stellar
mass content, and velocity dispersion all point to a collapsed, cluster-sized dark matter halo
with mass M 200c= 10 13.9±0.2 M⊙, making it the most distant X-ray-detected cluster …

We report the discovery of a remarkable concentration of massive galaxies with extended X-
ray emission at zspec= 2.506, which contains 11 massive (M*? 1011M?) galaxies in the
central 80-kpc region (11.6 s overdensity). We have spectroscopically confirmed 17 member
galaxies with 11 from CO and the remaining ones from Ha. The X-ray luminosity, stellar
mass content and velocity dispersion all point to a collapsed, cluster-sized dark matter halo
with mass M200c= 1013.9±0.2 M?, making it the most distant X-ray-detected cluster known …