We discuss the optical parameter space (luminosity and surface brightness) over which galaxies are known to exist and report on the results from three recent datasets: the Two-degree Field Galaxy Red-shift Survey, the Hubble Deep Field north, and the Local Group. These data are combined to provide a unique and comprehensive insight into the luminosity distribution of galaxies over the range −24...

Recent surveys have discovered hundreds of low surface brightness galaxies, systems with central surface brightness fainter than 22.0 B mag arcsec, in the local universe. Plots of the surface brightness distribution – that is, the space density of galaxies plotted against central surface brightness – show a flat space density distribution from the canonical Freeman value of 21.65 through the cu...