The structure of rapidly rotating late-type spiral galaxies. I. Photometry, HI, and optical kinematics

We present I-band photometry, long-slit optical spectroscopy, and new aperture synthesis H I observations for eight late-type spiral galaxies with rotation velocities in the range 243 km s(-1) less than or similar to V-rot less than or similar to 308 km s(-1). The sample will be used to study the structure and angular momentum of disks at the high- mass end of the spiral galaxy population; here we discuss the basic properties of these fast rotators'' and derive hybrid optical/H I rotation curves for each. Despite the presence of H I warps and low-mass companions in many systems, their kinematics are regular and there is excellent agreement between optical and H I tracers near the optical radius r(opt). At high inclinations at which projection effects are negligible, the sample galaxies exhibit flat, featureless rotation curves out to their last measured points at 1:7r(opt)-3: 5r(opt). The intermediate-inclination systems are also consistent with a constant rotation amplitude for r greater than or similar to 0.5r(opt). We therefore find no evidence for declining rotation curves at the high-mass end of the late-type spiral galaxy population. Combining our datawith the compilation of spiral galaxies with reliable outer H I kinematics from the work of Casertano and van Gorkom, we find no convincing trends between logarithmic outer rotation curve slopes and rotation amplitudes or surface brightnesses for galaxies with V-rot >= 220 km s(-1). Correlations between these slopes and morphological types or disk scale lengths are also marginal in this regime.