Internal Kinematics of Field Galaxies at Intermediate Redshifts

Low-mass starbursting galaxies have been proposed as the explanation of theexcess of faint galaxies observed at intermediate redshifts. If this hypothesisis correct, then intermediate redshift galaxies should rotate more slowly thannearby galaxies with the same rest-frame luminosity. We present the results ofa survey of the internal kinematics of intermediate redshift (z = 0.25-0.45)field galaxies to search for this effect. Using the Canada-France-HawaiiTelescope, spatially-resolved spectra of the [O II] $\lambda\lambda$ 3726- 3729\AA doublet emission line have been obtained for 22 galaxies. V$_{\rm rot} $sin i and [O II] disk scale lengths have been extracted from each galaxyspectrum using a Bayesian fitting technique. Galaxies in the sample are found to be $\sim$1.5-2.0 mag brighter thanexpected from their rotation velocity and the local Tully-Fisher (TF) relation.Low-mass galaxies exhibit a wider range of evolution relative to the TFrelation than high-mass galaxies. The main source of uncertainty in this resultis the large scatter in the local TF relation for late-type galaxies.Luminosity-dependent luminosity evolution neatly reconciles the lack ofevolution seen in other works with the results of our survey. It is also foundthat the overall properties of [OII] kinematics at intermediate redshifts arevaried. For example, 25% of the field galaxies in the sample have [OII]kinematics unrelated to rotation; [OII] emission is confined to the nucleus inmost of these galaxies. Anomalous kinematics is found to be related to thepresence of companions -- i.e. minor merger events. A Doppler ellipse similarto those found in local dwarf galaxies has been observed in a z = 0.35 galaxy,and may be interpreted as a supernova-driven supershell.Comment: 8 pages and 1 figure, AASTeX v4.0 2-column preprint style. Submitted to ApJ Letters. Also available through anonymous FTP at ftp://astroftp.phys.uvic.ca/pub/simard