The Tully-Fisher Relation in Cluster Cl 0024+1654 at z = 0.4^{* **}

Using moderate-resolution Keck spectra, we have examined the velocity profiles of 15 members of cluster Cl 0024+1654 at z = 0.4. WFPC2 images of the cluster members have been used to determine structural parameters, including disk sizes, orientations, and inclinations. We compare two methods of optical rotation curve analysis for kinematic measurements. Both methods take seeing, slit size and orientation, and instrumental effects into account and yield similar rotation velocity measurements. Four of the galaxies in our sample exhibit unusual kinematic signatures, such as noncircular motions. Our key result is that the Cl 0024 galaxies are marginally underluminous (0.50 ± 0.23 mag), given their rotation velocities, as compared to the local Tully-Fisher relation. In this analysis, we assume no slope evolution and take into account systematic differences between local and distant velocity and luminosity measurements. Our result is particularly striking considering that the Cl 0024 members have very strong emission lines and local galaxies with similar Hα equivalent widths tend to be overluminous on the Tully-Fisher relation. Cl 0024 Tully-Fisher residuals appear to be correlated most strongly with galaxy rotation velocities, indicating a possible change in the slope of the Tully-Fisher relation. However, we caution that this result may be strongly affected by magnitude selection and by the original slope assumed for the analysis. Cl 0024 residuals also depend weakly on color, emission-line strength and extent, and photometric asymmetry. In a comparison of stellar and gas motions in two Cl 0024 members, we find no evidence for counterrotating stars and gas, an expected signature of mergers.