Properties of the class of giant low surface brightness spiral galaxies

We have obtained CCD surface photometry and optical spectroscopy for a sample of eight giant low surface brightness (LSB) spiral galaxies discovered in the course of a large survey for LSB galaxies. We find that these LSB giants have disks of larger scale length and lower central surface brightness than other spiral galaxies, although none have parameters as extreme as the prototype Malin 1. We find that the integrated colors of these LSB giants are redder than the integrated colors of smaller LSB galaxies, and that the LSB galaxies of all sizes follow a relation between redder colors and increasing disk scale length. Two of these eight LSB giants have active nuclei with the broad permitted lines characteristic of a Seyfert 1 nucleus, and one has the narrow lines of a Seyfert 2. The colors and absorption line indices of the bulges of these giants are indistinguishable from those of HSB spirals, suggesting that their bulges have similar stellar populations and evolutionary histories. We also observed four and detected three of these galaxies in the 21 cm line of H I. These LSB giants generally have high total H I masses, although none is as extreme as Malin 1. Finally, the small-scale environments around these galaxies reveal several nearby companions. These LSB giants are at least as likely as smaller LSB galaxies to have close companions, and their average number of neighbors approaches that of HSB galaxies.