Compact Lyα-emitting candidates at z≃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 of compact Ly alpha emission objects around the radio galaxy 53W002 at z similar 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 widespread population at these redshifts. The three new fields contain 18 Ly alpha candidates, in contrast to the 17 detected in the deeper exposure of the single WFPC2 held around 53W002. We find substantial differences in the number of candidates from held to field, suggesting that significant large-scale structure is already present in the galaxy distribution at this cosmic epoch. The likely existence of z similar or equal to 2.4 subgalactic 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.