The Infrared Tully-Fisher Relation in the Ursa Major Cluster

We present new magnitudes derived from 1.65 micron images for 23 galaxies inthe Ursa Major cluster. Magnitudes now exist for all but one spiral meeting ourcriteria for cluster membership and having HI velocity width greater than 187km/s and inclination greater than 45 deg. These spirals fit a Tully-Fisherrelation with dispersion in intrinsic magnitudes (after known observationaluncertainties and the effect of cluster depth are removed) of 0.36 and a slopeof 10.2 +/- 0.6. The magnitude dispersion is smaller than found in the Virgocluster but still significantly larger than claimed by some authors. We find ahint that the Tully-Fisher relation may turn over at the bright end. Adding thecentral surface brightness of the disk as a third parameter flattens the slopeof the Tully- Fisher relation and may give a distance estimate with slightlyless dispersion, but the significance of the decrease must be tested on anindependent sample.Comment: 24, Latex, CfA-366