Dark matter in low surface brightness galaxies

Low Surface Brightness (LSB) galaxies form a large population of disc galaxies that extend the Hubble sequence towards extreme late-types. They are only slowly evolving, and still in an early evolutionary state. The Tully-Fisher relation and rotation curves of LSB galaxies both show that LSB galaxies are very dark-matter dominated with respect to "normal" high surface brightness (HSB) galaxies. Mass models derived from the rotation curves of LSB and HSB galaxies tentatively suggest that LSB galaxies inhabit less dense and more extended halos. Mass density, which changes with surface brightness, is as important in determining the evolution of a galaxy as total mass is.