Program: GS-2012A-Q-75

A crucial period in the evolution of current-day groups and clusters (and their galaxy populations) occurs at z>2. The clusters will be building up through mergers and the cluster galaxies will be actively forming stars at these redshifts. Unfortunately we have identified few systems at these redshifts that we can be sure are typical of the population. New simulations strongly indicate that bright high-z submillimeter galaxies (SMGs) trace progenitors of current-day groups and clusters, implying that targeting SMG fields will efficiently identify such systems in their early stages of evolution. As part of a programme to test whether bright z>2 SMGs do pick out groups and clusters in their early stages of evolution, we have targeted the field of the z=2.57 SMG J14011+0252 using narrow-band imaging in centred on redshifted Ly-alpha. The 5'x5' image identifies over 30 candidate Ly-alpha emitters Presently, only three near companions of the SMG are known to share its redshift. We now wish to target the rest of the candidate Ly alpha emitters spectroscopically with GMOS-S, in order to confirm these candidates and their clustering, and make an initial estimate of the dynamical state of this likely group or cluster in formation.