High and low surface brightness galaxies in the local universe. IV. Optical and 21 centimeter spectroscopy

We present flux-calibrated spectra in the range 3500 to 8000 Angstrom or th e nuclear regions of 250 galaxies and H I 21 cm line profiles for 238 galax ies selected from the catalog of low surface brightness galaxies identified in Automated Plate Measuring Facility (APM) scans of UK Schmidt Telescope survey plates. For the optical spectra, common nebular absorption- and emis sion-line equivalent widths and emission-line fluxes were measured with typ ical errors of about 20%. H I mass and velocity widths were measured from t he 21 cm line emission, with 15% accuracy. Galaxies in this study span over 6 mag in surface brightness. Only about 20% of these galaxies show spectro scopic evidence of active galactic nuclei. Derived quantities such as synth etic colors, metallicity, star formation rate, the ratio of neutral hydroge n mass to blue light, and gas mass fraction are presented in a companion pa per.