Caltech Faint Galaxy Redshift Survey. XIV. Galaxy Morphology in the Hubble Deep Field (North) and Its Flanking Fields to z = 1.2*

Morphological classifications are reported for Hubble Space Telescope (HST)images of 241 galaxies in the Hubble Deep Field (HDF) and its Flanking Fields(FF) with measured redshifts in the interval 0.25 < z < 1.2, drawn from amagnitude-limited redshift survey to R = 24.0. The galaxies are divided intothree groups with redshifts in the intervals [0.25,0.6], [0.6,0.8], [0.8,1.2].R606 images from the first group and I814 images from the second and thirdgroups are compared with B-band images of nearby galaxies. All classificationswere therefore made at approximately the same rest wavelength. Selection biasesare discussed. We corroborate and extend the results of earlier investigationsby observing that: Most intermediate and late-type galaxies with $z\gtrsim0.5$have morphologies that are dramatically different from those of local galaxiesand cannot be shoehorned into the Hubble ``tuning fork'' classification scheme.Grand-design spirals appear to be rare or absent for $z\gtrsim0.3$. Many Sa andSb spirals with $z\gtrsim0.6$ do not exhibit well-defined spiral arms. The armsof distant Sc galaxies appear more chaotic than those of their nearbycounterparts. (abridged) On the basis of these and similar observations, it isinferred that the development of pronounced spiral structure was delayed until\~5 Gyr and that most bulges are probably not formed by disintegrating bars.Major morphological changes were still taking place only ~5 Gyr ago even thoughchanges in the integrated light of most galaxies were then much slower thanthey were ~10 Gyr ago.Comment: Accepted by the Astronomical Journa