THE TULLY-FISHER RELATION FOR LOW SURFACE BRIGHTNESS GALAXIES - IMPLICATIONS FOR GALAXY EVOLUTION

We present the B-band Tully-Fisher relation for low surface brightness (LSB) galaxies. These LSB galaxies follow the same Tully-Fisher relat ion as normal spiral galaxies. This implies that the mass-to-light rat io (M/L) of LSB galaxies is typically a factor of 2 larger than that o f normal galaxies of the same total luminosity and morphological type. Since the dynamical mass of a galaxy is related to the rotational vel ocity and scalelength via M proportional to V(2)h, at fixed linewidth LSB galaxies must be twice as large as normal galaxies. This is confir med by examining the relation between scalelength and linewidth for LS B and normal galaxies. The universal nature of the Tully-Fisher relati on can be understood if LSB galaxies are galaxies with low mass surfac e density, sigma ($) over bar. The mass surface density apparently con trols the luminosity evolution of a galaxy in such a way as to keep th e product sigma ($) over bar M/L constant.