THE NEAR-INFRARED TULLY-FISHER RELATION - A PRELIMINARY-STUDY OF THE COMA AND ABELL-400 CLUSTERS

We have started a large project to study the near-infrared luminosity- linewidth (Tully-Fisher) relation using H- and I-band surface photomet ry of spiral galaxies. A preliminary study of 20 spirals in the Coma a nd Abell 400 clusters (both at approximately 7000 km s-1) is presented . The near-infrared images have been used to derive accurate inclinati ons and total magnitudes, and rotational linewidths are measured from high-quality 21-cm Arecibo data. The scatter in the Coma Tully-Fisher plot is found to be 0. 19 mag in the H band and 0.20 mag in the I band for a set of 13 galaxies, if we assume that they are all at the same distance. The deviation of the Coma galaxies from the best-fit Tully-F isher relation is correlated with their redshift, indicating that some of the galaxies are not bound to the cluster. Indeed, if we treat all the galaxies in the Coma sample as undergoing free Hubble expansion, the Tully-Fisher scatter drops to 0.12 and 0.13 mag for the H- and I-b and datasets, respectively. The Abell 400 sample is best fit by a comm on distance model, yielding a scatter of 0.12 mag for seven galaxies i n H using a fixed Tully-Fisher slope (derived from our Coma H sample). We are in the process of studying cluster and field spirals out to ap proximately 10,000 km s-1 in order to calibrate the near-infrared Tull y-Fisher relation and will apply it to more nearby galaxies to measure the peculiar velocity field (and hence the mass distribution) in the local Universe.