SBF Distances to Leo and Virgo using the HST

We have used archive HST WFPC2 data for three elliptical galaxies (NGC 3379 in the Leo I group, and NGC 4472 and NGC 4406 in the Virgo cluster) to determine their distances using the Surface Brightness Fluctuation (SBF) method as described by Tonry and Schneider (1988). A comparison of the HST results with the SBF distance moduli of Ciardullo et al (1993) shows significant disagreement and suggests that the r.m.s. error on these ground-based distance moduli is actually as large as +-0.25 mag. The agreement is only slightly improved when we compare our results with the HST and ground-based SBF distances from Ajhar et al (1997) and Tonry et al (1997); the comparison suggests that a lower limit on the error of the HST SBF distance moduli is +-0.17 mag. Overall, these results suggest that previously quoted measurement errors may underestimate the true error in SBF distance moduli by at least a factor of 2-3.