  We present deep wide-field medium-band imaging in redshifted Lyman alpha of
fields surrounding HST detections of faint emitters, to characterize their
larger-scale environment. The radio galaxy 53W002 was previously found to be
part of a rich grouping at z=2.39, including 5 confirmed, compact, star-forming
objects. This is now shown to be part of a larger structure traced by bright
AGN, all contained within a projected span of 6.8 arcmin (3.2 Mpc). Of the 14
candidate emitters, six have been spectroscopically confirmed as active nuclei
in the range z=2.390 +/- 0.008. Various statistical tests give a significance
of 95-99% for the reality of this structure on the sky. This grouping is more
extended than a relaxed King model, at the 90% confidence level. Either this
configuration has yet to decouple fully from the Hubble expansion, or it
consists of subgroups which will themselves form a more compact, relaxed
structure. The redshift range for measured members is comparable to the Hubble
flow across the structure, which may imply that the structure is seen near
turnaround.
  We surveyed two additional fields at z=2.4, and three contiguous fields at
z=2.6. Only a single candidate at z=2.4 was found, with six at z=2.6.
Comparison with the WFPC2 surveys suggests that the field-to-field contrast is
larger for brighter objects. From this survey alone, groupings such as the
53W002 "cluster" must have an area covering fraction <0.04 in this redshift
range.
