A mature cluster with X-ray emission at z = 2.07 R. Gobat, E. Daddi, M. Onodera, A. Finoguenov, A. Renzini, N. Arimoto, R. Bouwens, M. Brusa, R.-R. Chary, A. Cimatti et al. (3 more) A&A, 526 (2011) A133 Published online: 11 January 2011 DOI: 10.1051/0004-6361/201016084