  A homogeneous sample of ~2200 low redshift disk galaxies with both high
sensitivity long-slit optical spectroscopy and detailed I-band photometry is
used to construct average, or template, rotation curves in separate luminosity
classes, spanning 6 magnitudes in I-band luminosity. The template rotation
curves are expressed as functions both of exponential disk scale lengths r_d
and of optical radii Ropt, and extend out to 4.5-6.5 r_d, depending on the
luminosity bin. The two parameterizations yield slightly different results
beyond Ropt because galaxies whose Halpha emission can be traced to larger
extents in the disks are typically of higher optical surface brightness and are
characterized by larger values of Ropt/r_d. By either parameterization, these
template rotation curves show no convincing evidence of velocity decline within
the spatial scales over which they are sampled, even in the case of the most
luminous systems. In contrast to some previous expectations, the fastest
rotators (most luminous galaxies) have, on average, rotation curves that are
flat or mildly rising beyond the optical radius, implying that the dark matter
halo makes an important contribution to the kinematics also in these systems.
The template rotation curves and the derived functional fits provide
quantitative constraints for studies of the structure and evolution of disk
galaxies, which aim at reproducing the internal kinematics properties of disks
at the present cosmological epoch.
