The Tully-Fisher Zero Point Problem

Abstract

A long standing problem for hierarchical disk galaxy formation models has been the simultaneous matching of the zero point of the Tully-Fisher relation and the galaxy luminosity function (LF). We illustrate this problem for a typical disk galaxy and discuss three solutions: low stellar mass-to-light ratios, low initial dark halo concentrations, and no halo contraction. We speculate that halo contraction may be reversed through a combination of mass ejection through feedback and angular momentum exchange brought about by dynamical friction between baryons and dark matter during the disk formation process.Comment: 4 pages, 1 figure, to appear in proceedings of "Formation and Evolution of Galaxy Disks", Rome, October 2007, Eds. J.G. Funes, S.J. and E.M. Corsin