2000A&A...361L..25P

VLT spectroscopic observations of Lyα-excess objects in the field of the clumpy radio galaxy 1138-262 at z=2.16 have led to the discovery of 14 galaxies and one QSO at approximately the same distance as the radio galaxy. All galaxies have redshifts in the range 2.16±0.02, centered around the redshift of the radio galaxy, and are within a projected physical distance of 1.5Mpc from it. The velocity distribution suggests that there are two galaxy subgroups having velocity dispersions of ∼500km/s and ∼300km/s and a relative velocity of 1800km/s. If these are virialized structures, the estimated dynamical masses for the subgroups are ∼9 and ∼3x10¹³M_☉ respectively, implying a total mass for the structure of more than 10¹⁴M_☉. The new observations, together with previous results, suggest that the structure of galaxies around 1138-262 is likely to be a forming cluster.