Spatially Resolved Kinematics of Distant Galaxies

Abstract

A Tully-Fisher (TF) relation from H-alpha rotation curves of 19 luminous, star-forming galaxies reveals there is little evidence for evolution in the mass-to-light ratio (M/L) of these galaxies to z~0.3. The near-infrared Tolman surface-brightness test for other luminous galaxies indicates their luminosity also is little changed to z~0.3. In this redshift regime, internal velocity -- luminosity relations like Tully-Fisher may provide a way to measure q0. Discrepant results from several intermediate redshift Tully-Fisher surveys, however, must be understood first. One possibility is that different surveys sample different galaxy types and TF relations. Alternatively, M/L of some spiral galaxies may evolve rapidly with look-back time. Larger surveys are needed to resolve this issue. A different approach is to determine disk and halo M/L separately. Such measurements, even at low redshift, would be sensitive to the star formation histories of disks. We outline plans for lambda/dlambda ~ 10000 integral-field spectroscopy of relatively face-on spirals using the 9m Hobby-Eberly Telescope. Rotation curves and disk stellar velocity dispersions can provide statistical information about the M/L of dark halos as well as luminous disks.