THE MORPHOLOGY OF FAINT GALAXIES IN MEDIUM DEEP SURVEY IMAGES USING WFPC2

First results from HST Medium Deep Survey images taken with WFPC2 demo nstrate that galaxy classifications can be reliably performed to magni tudes I814 less-than-or-similar-to 22.0 in the F815W band. Published s pectroscopic surveys to this depth indicate a mean redshift of zBAR ap proximately 0.5. We have classified over 200 galaxies in nine WFPC2 fi elds according to a basic morphological scheme. The majority of these faint galaxies appear to be similar to regular Hubble-sequence example s observed at low redshift. To the precision of our classification sch eme, the relative proportion of spheroidal and disk systems of normal appearance is as expected from nearby samples, indicating that the bul k of the local galaxy population was in place at half the Hubble time. However, the most intriguining result the relatively high proportion (approximately 40%) of objects which are in some way anomalous, and wh ich may be of relevance in understanding the origin of the familiar ex cess population of faint galaxies established by others. These diverse objects include apparently interacting pairs whose multiple structure is only revealed with HST's angular resolution, galaxies with superlu minous star-forming regions, diffuse low surface brightness galaxies o f various forms, and compact galaxies. These anomalous galaxies contri bute a substantial fraction of the excess counts at our limiting magni tude, and may provide insights into the ''faint blue galaxy'' problem.