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 newaperture synthesis HI observations for eight late-type spirals with rotationvelocities in the range 243 km/s < V_{rot} < 308 km/s. The sample will be usedto study the structure and angular momentum of disks at the high-mass end ofthe spiral galaxy population; here we discuss the basic properties of these``fast rotators'', and derive hybrid optical/HI rotation curves for each.Despite the presence of HI warps and low-mass companions in many systems, theirkinematics are regular and there is excellent agreement between optical and HItracers near the optical radius r_{opt}. At high inclinations at whichprojection effects are negligible, the sample galaxies exhibit flat,featureless rotation curves out to their last measured points at1.7r_{opt}--3.5 r_{opt}. The intermediate inclination systems are alsoconsistent with a constant rotation amplitude for r > 0.5 r_{opt}. We thereforefind no evidence for declining rotation curves at the high-mass end of thelate-type spiral galaxy population. Combining our data with the compilation ofspirals with reliable outer HI kinematics from the work of Casertano & vanGorkom, we find no convincing trends between logarithmic outer rotation curveslopes and rotation amplitudes or surface brightnesses for galaxies withV_{rot} > 220 km/s. Correlations between these slopes and morphological typesor disk scale lengths are also marginal in this regime.