The Tully-Fisher relation of distant cluster galaxies

We have measured maximum rotation velocities (V-rot) for a sample of 111 emission-line galaxies with 0.1 less than or similar to z less than or similar to 1, observed in the fields of six clusters. From these data we construct 'matched' samples of 58 field and 22 cluster galaxies, covering similar ranges in redshift (0.25 <= z <= 1.0) and luminosity (M-B<=-19.5 mag), and selected in a homogeneous manner. We find the distributions of M-B, V-rot and scalelength to be very similar for the two samples. However, using the Tully-Fisher relation (TFR) we find that cluster galaxies are systematically offset with respect to the field sample by 0.7 +/- 0.2 mag. This offset is significant at 3 sigma and persists when we account for an evolution of the field TFR with redshift. Extensive tests are performed to investigate potential differences between the measured emission lines and derived rotation curves of the cluster and field samples. However, no such differences that could affect the derived V-rot values and account for the offset are found. The most likely explanation for the TFR offset is that giant spiral galaxies in distant clusters are on average brighter, for a given rotation velocity, than those in the field. This could be due to enhanced star formation caused by an initial interaction with the intracluster medium. As our selection favours galaxies with strong emission lines, this effect may not apply to the entire cluster spiral population, but does imply that strongly star-forming spirals in clusters are more luminous than those in the field, and possibly have higher star formation rates. However, the possibility that this TFR offset is a mass-related effect, e.g. due to the stripping of galaxy dark matter haloes, is not excluded by our data.