The Formation of Low Surface Brightness Galaxies

The formation of low surface brightness galaxies is an unavoidable prediction of any hierarchical clustering scenario. In these models, low surface brightness galaxies form at late times from small initial overdensities, and make up most of the faint end of the galaxy luminosity function. Because there are tremendous observational biases against finding low surface brightness galaxies, the observed faint end of the galaxy luminosity function may easily fall short of predictions, if hierarchical structure formation is correct. We calculate the number density and mass density in collapsed objects as a function of baryonic surface density and redshift, and show that the mass in recently formed low surface brightness galaxies can be comparable to the mass bound into “normal” high surface brightness galaxies. Because of their low gas surface densities, these galaxies are easily ionized by the UV background and are not expected to appear in HI surveys. Low surface brightness galaxies (LSBs) are not a special case of galaxy formation and are perhaps better viewed as a continuance of the Hubble sequence.