dynamics and star formation and assembly history. For spiral galaxies in general, morphology can be understood in terms of bulge-to-disk ratios. Dynamically, the growth of a bulge in the center of a disk is the result of secular (angular momentum redistribution and stellar migration, bars) and violent (mergers) processes, all of which leave a trace in the galaxy rotation curve. At the same time, the star formation history of the galaxy, which is affected by the dynamical evolution, imprints the bulge-to-disk luminosity. A theoretical determination of the TF relation needs to incorporate each of these effects to be successful, a job that hierarchical semi-analytic models are best suited to accomplish.

Which radius? An angular momentum problem
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When studying the morphology dependence of the TF relation, it becomes especially important to measure the TF at a meaningful, physically motivated radius. Because of the different radial profiles of the galaxy dynamical components (disk, bulge, dark matter halo, gas), *1)* the slope of the TF relation varies with the radius at which the rotation velocity is calculated (Yegorova et al. 2007) and *2)* the same radius in galaxies of different morphology probes different dynamical regions, thus introducing an artificial scatter in the 