HUBBLE-SPACE-TELESCOPE IMAGING OF THE CFRS AND LDSS REDSHIFT SURVEYS - I - MORPHOLOGICAL PROPERTIES

We analyze Hubble Space Telescope images of a complete sample of 341 g alaxies drawn from the CFRS and LDSS ground-based redshift surveys. In this, the first paper in the series, each galaxy has been morphologic ally classified according to a scheme similar to that developed for th e Medium Deep Survey. We discuss the reproducibility of these classifi cations and quantify possible biases that may arise from various redsh ift-dependent effects. We then discuss automated classifications of th e sample and conclude, from several tests, that we can expect an appar ent migration with redshift to later Hubble types that corresponds to a misclassification in our adopted machine classification system of si milar to 24% +/- 11 of the true ''spirals'' as ''peculiars'' at a reds hift z similar or equal to 0.9. After allowing for such biases, the re dshift distribution for normal spirals, together with their luminosity function derived as a function of redshift, indicates approximately 1 mag of luminosity evolution in B-AB by z similar or equal to 1. The e lliptical sample is too small for precise evolutionary constraints. Ho wever, we find a substantial increase in the proportion of galaxies wi th irregular morphology at large redshift from 9% +/- 3% for 0.3 less than or equal to z less than or equal to 0.5 to 32% +/- 12% for 0.7 le ss than or equal to z less than or equal to 0.9. These galaxies also a ppear to be the dominant cause of the rapid rise with redshift in the blue luminosity density identified in the redshift surveys. Although g alaxies with irregular morphology may well comprise a mixture of diffe rent physical systems and might not correspond to present-day irregula rs, it is clear that the apparently declining abundance and luminositi es of our distant ''irregulars'' holds an important key to understandi ng recent evolution in the star formation history of normal galaxies.