The stellar and gaseous content of massive low surface brightness disk galaxies

This dissertation presents a multi-wavelength study of a subset of an extreme type of galaxy, those which have low surface brightnesses large disks, and large amounts of atomic gas, yet which have total dynamical masses similar to those of giant spiral galaxies. These systems may represent a significant, but largely unexplored, fraction of galaxies in the universe, and determining their star formation histories and evolution is critical to our attempts to understand the different modes of formation and evolution of all galaxies. Surface photometry at B and R, in conjunction with H$\sb{\rm I}$, $\sp{12}$CO and far-infrared data, is used to try to determine if these galaxies had an early epoch of star formation that has since faded, have ongoing star formation with an unusual IMF, or are perhaps galaxies which have never efficiently formed stars due to a lack of molecular clouds. Results of our observations confirm earlier findings that these systems in general have very blue disks relative to higher surface brightness, gas-rich disk systems. This result makes it very difficult to explain these galaxies as faded disks. Although they have prodigious amounts of H$\sb{\rm I}$, there is little evidence of abundant $\sp{12}$CO or dust. Despite their physical similarities, they show an amazing variety of optical morphologies. Many have steep radial color gradients, perhaps due to changing metallicities. These systems tend to be in fairly isolated regions of the universe. The lack of nearby neighbors may have allowed them to form and evolve in a very different manner from typical high surface brightness galaxies. Some systems may, in fact, have undergone very little star formation over time. If this is true, this population could represent a valuable window into the early epochs of star formation in disk galaxies