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

Abstract

ABSTRACT We have started a large project to study the near-infrared luminosity-linewidth (Tully-Fisher) relation using H- and I-band surface photometry of spiral galaxies. A preliminary study of 20 spirals in the Coma and Abell 400 clusters (both at ~7000 km s-1) is presented. The near-infrared images have been used to derive accurate inclinations and total magnitudes, and rotational line widths 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-Fisher 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 mag and 0.13 mag for the H- and I-band datasets, respectively. The Abell 400 sample is best fit by a common distance model, yielding a scatter of 0.12 mag for seven galaxies in H using a fixed Tully-Fishr slope (derived from our Coma H sample). We are in the process of studying cluster and field spirals out to ~10,000 km s-1 in order to calibrate the near-infrared Tully-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.