SFI++I: A New I‐Band Tully‐Fisher Template, the Cluster Peculiar Velocity Dispersion, and H0

Abstract

The SFI++ consists of ~5000 spiral galaxies that have measurements suitable for the application of the I -band Tully-Fisher (TF) relation. This sample builds on the SCI and SFI samples published in the 1990s but includes significant amounts of new data, as well as improved methods for parameter determination. We derive a new I -band TF relation from a subset of this sample, which consists of 807 galaxies in the fields of 31 nearby clusters and groups. This sample constitutes the largest ever available for the calibration of the TF template and extends the range of line widths over which the template is reliably measured. Careful accounting is made of observational and sample biases such as incompleteness, finite cluster size, galaxy morphology, and environment. We find evidence for a type-dependent TF slope that is shallower for early-type than for late-type spirals. The line-of-sight cluster peculiar velocity dispersion is measured for the sample of 31 clusters. This value is directly related to the spectrum of initial density fluctuations and thus provides an independent verification of the best-fit WMAP cosmology and an estimate of Ω 0.6 σ 8 = 0.52 ± 0.06. We also provide an independent measure of the TF zero point using 17 galaxies in the SFI++ sample for which Cepheid distances are available. In combination with the "basket-of-clusters" template relation these calibrator galaxies provide a measure of H 0 = 74 ± 2 (random) ±6 (systematic) km s -1 Mpc -1 .