A physical distance indicator for spiral galaxies

In this paper we derive a Tully Fisher relation from measured I band photometry and H$\alpha$ rotation curves of a large survey of southern sky spiral galaxies, obtained in Persic \& Salucci (1995) by deprojecting and folding the raw H$\alpha$ data of Mathewson, Ford \& Buchhorn (1992). We calibrate the relation by combining several of the largest clusters in the survey, using an iterative maximum likelihood procedure to account for observational selection effects and Malmquist bias. We also incorporate a simple model for the line of sight depth of each cluster. Our results indicate a Tully Fisher relation of intrinsic dispersion $\sim0.3$ mag, corresponding to a distance error dispersion of $13\%$. Application of this relation to mapping the large scale velocity field is underway.