Gas, Stars and Baryons in Low Surface Brightness Galaxies

Recent surveys have discovered hundreds of low surface brightness galaxies in the local (z < 0.1) Universe. Plots of the surface brightness distribution (the space density of galaxies plotted against central surface brightness) show a flat distribution from the bright-end cutoff of 21.65 through the current observational limit of 25.0 B mag arcsec^{-2}. As no trend is seen to indicate the size or mass of galaxies decreases with decreasing central surface brightness, it is likely that a significant percentage of the baryon content in the universe is contained in these diffuse systems. In this paper I briefly review the known properties of low surface brightness galaxies, and describe some current theories on the baryonic mass fraction of low surface brightness systems and their consequences.