The Photometric and Kinematic Structure of Face-on Disk Galaxies. I. Sample Definition, Hα Integral Field Spectroscopy, and H I Line Widths

We present a survey of the photometric and kinematic properties of 39 nearby, nearly face-on disk galaxies. Our approach exploits echelle-resolution integral-field spectroscopy of the Hα regions, obtained with DensePak on the WIYN 3.5 m telescope Bench Spectrograph. These data are complemented by H I line profiles observed with the Nançay radio telescope for 25 of these sample galaxies. Twelve additional line widths are available for sample galaxies from the literature. In this paper, we introduce the goals of this survey, define the sample selection algorithm, and amass the integral field spectroscopic data and H I line widths. We establish spatially integrated Hα line widths for the sample. We test the veracity of these spatially integrated line profiles by convolving narrowband imaging data with velocity field information for one of the sample galaxies, PGC 38268, and also by comparing to H I line profiles. We find H I and Hα line profiles to be similar in width but different in shape, indicating that we are observing different spatial distributions of ionized and neutral gas in largely axisymmetric systems with flat outer rotation curves. We also find vertical velocity dispersions of the ionized disk gas within several disk scale lengths have a median value of 18 km s-1 and an 80% range of 12-26 km s-1. This is only a factor of ~2 larger than what is observed for neutral atomic and molecular gas. With standard assumptions for intrinsic and thermal broadening for Hα, this translates into a factor of 3 range in turbulent velocities, between 8 and 25 km s-1.