NAME NGC 6899 Group , the SIMBAD biblio

The Tully-Fisher relationship is subject to morphological type dependence such that galaxies of morphology similar to Sc I galaxies and Seyfert galaxies are more luminous at a given rotational velocity than galaxies of other morphological classification. This effect is most prevalent in the B band. It is shown that the type effect is not simply an artifact of the calibrator sample but is also present in cluster samples. The type effect is corrected by creating type-dependent Tully-Fisher relations for Sc I group galaxies and Sb/Sc III group galaxies. It is shown that with single calibrations, the distances to Sc I group galaxies are systematically underestimated, while the distances to Sb/Sc III group galaxies are systematically overestimated. Tully-Fisher slope and scatter are also considered in the context of type-dependent Tully-Fisher relations. It is concluded that the use of type-dependent Tully-Fisher relations provides significant improvement in the distances to individual galaxies and the refined distances to clusters of galaxies.