Optical Rotation Curves of Distant Field Galaxies: Sub-L⋆ Systems

Moderate-resolution spectroscopic observations from the Keck 10 m telescope are used to derive internal kinematics for eight faint disk galaxies in the fields flanking the Hubble Deep Field. The spectroscopic data are combined with high-resolution F814W Wide Field Planetary Camera 2 images from the Hubble Space Telescope that provide morphologies, scale lengths, inclinations, and orientations. The eight galaxies have redshifts 0.15 ≲ z ≲ 0.75, magnitudes 18.6 ≤ I814 ≤ 22.1, and luminosities -21.8 ≤ MB ≤ -19.0 (H0 = 75 km s-1 Mpc-1 and q0 = 0.05). Terminal disk velocities are derived from the spatially resolved velocity profiles by modeling the effects of seeing, slit width, slit misalignment with galaxy major axis, and inclination for each source. These data are combined with the sample of Vogt et al. to provide a high-redshift Tully-Fisher relation that spans 3 magnitudes. This sample was selected primarily by morphology and magnitude, rather than color or spectral features. We find no obvious change in the shape or slope of the relation with respect to the local Tully-Fisher relation. The small offset of ≲0.4 mag in B with respect to the local relation is presumably caused by luminosity evolution in the field galaxy population and does not correlate with galaxy mass. A comparison of disk surface brightness between local and high-redshift samples yields a similar offset, ~0.6 mag. These results provide further evidence for only a modest increase in luminosity with look-back time.