It is unlikely to be gravitationally bound, and so would not meet most low redshift definitions of a galaxy cluster. All three have reliable spectroscopic redshifts. Clearly the space density of Ly emitting galaxies in this region is higher than average. 3D view of the 2142-4420 cluster. All objects have been assigned 3-dimensional positions, based on their location on the sky and their redshift, assuming that all redshifts trace the Hubble Flow.
Solid lines are the sight-lines to the three background QSOs.
Stars are Ly-limit absorption systems, crosses are the lower column density absorption systems, and solid triangles are the Ly emitting galaxies. 1 should make the geometry of the cluster clearer. The three Ly galaxies lie within one Mpc of each other. The absorption-line systems are far more dispersed, extending both to lower redshifts and transversely by Mpc. The total exposure time was 47,700 sec, and the spectral resolution 700 .