Rotation curve shapes and the Tully-Fisher relations

The scatter in the K'-band Tully-Fisher relation (TFr) is larger than can be expected from observational uncertainties when using the widths of global HI profiles of a volume limited, complete sample without any morphological selection criteria. This poster shows, however, that the observed scatter can be explained when considering the shapes of the galaxy rotation curves (RCs). Using V(m)ax from the RCs, it turns out that galaxies with rising RCs tend to lie on the low-velocity side of the TFr and those with declining RCs tend to lie on the high velocity side. The scatter in the K'-V-flat TFr is consistent with the measurement uncertainties.