Compact Lyman-alpha Emitting Candidates at z~2.4 in Deep Medium-band HST   WFPC2 Images
  Medium-band imaging with HST/WFPC2 in the F410M filter has previously revealed a population of compact Lyman-alpha emission objects around the radio galaxy 53W002 at z~2.4. We report detections of similar objects at z~2.4 in random, high-latitude HST parallel observations of three additional fields, lending support to the idea that they constitute a widespread population at these redshifts. The three new fields contain 18 Lyman-alpha candidates, in contrast to the 17 detected in the deeper exposure of the single WFPC2 field around 53W002. We find substantial differences in the number of candidates from field to field, suggesting that significant large-scale structure is already present in the galaxy distribution at this cosmic epoch. The likely existence of z~2.4 sub-galactic clumps in several random fields shows that these objects may have been common in the early universe and strengthens the argument that such objects may be responsible for the formation of a fraction of the luminous present-day galaxies through hierarchical merging. 
Sebastian M. Pascarelle, Rogier A. Windhorst, and William C. Keel