The baryonic Tully-Fisher relation

We explore the Tally-Fisher relation over five decades in stellar mass in g alaxies with circular velocities ranging over 30 less than or similar to V- c less than or similar to 300 km s(-1). We find a clear break in the optica l Tully-Fisher relation: held galaxies with V-c less than or similar to 90 km s(-1) fall below the relation defined by brighter galaxies. These faint galaxies, however, are very rich in gas; adding in the gas mass and plottin g the baryonic disk mass M-d = M* + M-gas in place of luminosity restores t he single linear relation. The Tully-Fisher relation thus appears fundament ally to be a relation between rotation velocity and total baryonic mass of the form M-d proportional to V-c(4).