[O II] internal kinematics has been measured in a sample of 22 intermediate redshift galaxies. A number of conclusions can be drawn from this survey:
=1 The synthetic rotation curve method provides a way to optimally extract the best parameter values allowed by the noise from low S/N data. With bigger telescopes and more efficient CCD detectors, this method will be invaluable to study high redshift objects which are not as [OII] strong and hence more representative of the local normal galaxy population.
=1 [OII] kinematics at intermediate redshifts is varied. 25 of the field galaxies in the sample had anomalous kinematics. In some of these galaxies, all of the [OII] emission was confined to the nucleus (as in local galaxies harboring active galactic nuclei), and the [OII] linewidth had no relation to galaxy rotation. In one kinematically anomalous galaxy, the [OII] emission may be coming from a galactic super shell which bears a striking resemblance to shells observed in local dwarf irregular galaxies. It is interesting that peculiarities in internal kinematics have local counterparts. Anomalous galaxies appear to be associated with minor merger events, and at least two galaxies appear to be early-types.
=1 Based on the absolute calibration of the Tully-Fisher relation, galaxies in the sample are 1.52.0 magnitudes brighter than expected for their rotation velocity. Relatively low-mass galaxies with V of 100 km/s exhibit a wider range of offsets from the Tully-Fisher relation. This is against arguments for uniform luminosity evolution.
=1 There is considerable scatter in the local Tully-Fisher relation especially for late-type spiral galaxies. There is insufficient local data (e.g. equivalent widths for a truly large and homogeneous sample) to determine whether most of this scatter comes from variations in star formation rates. Since local star-forming galaxies may be systematically brighter than expected from the local TF relation for normal galaxies, the magnitude of the magnitude offset seen in [OII] strong galaxies at intermediate redshifts may be reduced.
=1 A comparison with other works, notably spectroscopy obtained with the Keck telescope and CNOC surface brightness measurements, indicates the available evidence is best explained by luminosity-dependent luminosity evolution. Large, bright galaxies have rotation curves similar to local normal galaxies and show no evidence of an offset from the Tully-Fisher. On the other hand, the internal kinematics of small, low-mass objects are more varied and display a significant Tully-Fisher offset.
The future prospects for internal kinematics are very exciting. On the local front, the dependence of the local Tully-Fisher relation on variations in star formation rates must be investigated. The conclusions of all internal kinematics studies at high redshifts will critically depend on that aspect of the local TF relation as long as technical requirements restrict them to strong emission-line objects.
Properties of kinematically anomalous galaxies such as color, surface brightness profiles, [OII] equivalent widths and diagnostic emission line ratios need to be studied for a larger sample to confirm that merger events in early and late type galaxies may be triggering star formation in the nuclei of some intermediate redshift galaxies.
Current samples cannot be used to determine how the Tully-Fisher zero-point shifts as a function of redshift. The samples are small, and they are spread over a wide range of redshifts. However, it does appear that the TF slope does not remain constant under the effect of luminosity-dependent luminosity evolution, and larger samples are needed to measure luminosity changes as a function of redshift and galaxy mass. The dispersion in L at a given mass could be used to look for correlations with other parameters such as star formation rate.
Galaxies with [OII] substructures should be imaged with very high spatial resolution with the Hubble Space Telescope and ground-based adaptive optics systems such as the CFHT Adaptive Bonnette to find out what kind of morphological distortions are associated with those [OII] substructures.
It would also be possible with integral field spectrographs such as Fabry-Perot interferometers and fibre bundles to measure the electron density and [O/H] abundance using diagnostic line ratios (e.g. McGaugh mac91) as a function of position within intermediate redshift galaxies. Maps of N and [O/H] would be extremely valuable to understanding ionization processes and ISM enrichment mechanisms at work in distant galaxies.