Compact Ly alpha-emitting candidates at z similar or equal to 2.4 in deep medium-band Hubble Space Telescope WFPC2 images

Medium-band imaging with Hubble Space Telescope (HST) Wide Field Planetary Camera 2 (WFPC2) in the F410M filter has previously revealed a population o f compact Ly alpha emission objects around the radio galaxy 53W002 at z sim ilar or equal to 2.4. We report detections of similar objects at z similar or equal to 2.4 in random, high-latitude HST parallel observations of three additional fields, lending support to the idea that they constitute a wide spread population at these redshifts. The three new fields contain 18 Ly al pha candidates, in contrast to the 17 detected in the deeper exposure of th e single WFPC2 held around 53W002. We find substantial differences in the n umber of candidates from held to field, suggesting that significant large-s cale structure is already present in the galaxy distribution at this cosmic epoch. The likely existence of z similar or equal to 2.4 subgalactic clump s 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 r esponsible for the formation of a fraction of the luminous present-day gala xies through hierarchical merging.