Caltech Faint Galaxy Redshift Survey. XV. Classifications of Galaxies with 0.2 < z < 1.1 in the Hubble Deep Field North and its Flanking Fields

Abstract

To circumvent the spatial effects of resolution on galaxy classification, the images of 233 objects of known redshift in the Hubble Deep Field (HDF) and its flanking fields that have redshifts in the range 0.20 < z < 1.10 were degraded to the resolution that they would have had if they were all located at a redshift of z = 1.00. As in Paper XIV of the present series, the effects of shifts in rest wavelength were mitigated by using R-band images for the classification of galaxies with 0.2 < z < 0.6 and I-band images for objects with redshifts 0.6 < z < 1.1. A special effort was made to search for bars in distant galaxies. The present data strongly confirm the previous conclusion that the Hubble tuning fork diagram only provides a satisfactory framework for the classification of galaxies with z < 0.3. More distant disk galaxies are often difficult to shoehorn into the Hubble classification scheme. The paucity of barred spirals and grand-design spirals at large redshifts is confirmed. It is concluded that the morphology of disk galaxies observed at look-back times smaller than 3–4 Gyr differs systematically from that of more distant galaxies viewed at look-back times of 4–8 Gyr. The disks of late-type spirals at z > 0.5 are seen to be more chaotic than those of their nearer counterparts. Furthermore, the spiral structure in distant early-type spirals appears to be less well developed than it is in nearby early galaxies.

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