Internal kinematics of field galaxies at intermediate redshifts

This paper describes the results of a survey of the internal kinematics of intermediate-redshift (z = 0.25-0.45) field galaxies. Spatially resolved spectra of the [O II] lambda lambda 3726, 3729 doublet emission line have been obtained for 22 galaxies at the Canada-France-Hawaii Telescope. High spatial resolution has made it possible to extract V-rot sin i and [O II] disk scale lengths from each galaxy spectrum using synthetic galaxy rotation curve fitting. About 25% of the galaxies in the sample have [O II] kinematics unrelated to rotation. [O II] emission is concentrated in the nucleus in these "kinematically anomalous" galaxies. A Doppler ellipse, similar to those found in local dwarf irregular galaxies, has been observed in a z = 0.35 galaxy. An intermediate-redshift Tully-Fisher (TF) relation, defined by 12 kinematically normal galaxies, shows that these galaxies have a systematically lower rotation velocity (i.e., mass) for their luminosity than expected from the local TF relation. These galaxies would have to fade by similar to 1.5-2 mag to lie on the local TF relation. This is consistent with starbursting dwarf galaxy models. Although the sample is small, there is also a hint that massive galaxies are not as displaced from the local TF relation as low-mass ones. However, as shown using a large sample of local galaxies, the scatter in the local TF relation is large, especially for late-type galaxies. Sample selection effects, particularly in [O II] emission strength, could be responsible for part of the observed TF evolutionary shift if star formation rates were responsible for the local TF relation scatter. A comparison with other works indicates that a mass-dependent luminosity evolution scenario can explain almost all of the available internal kinematics and surface brightness data.