SBF distances to Leo and Virgo using the HST

Abstract

We use archive HST WFPC2 data for three elliptical galaxies (NGC 3379 in the Leo I group, and NGC 4472 and 4406 in the Virgo cluster) to determine their distances using the surface brightness fluctuation (SBF) method as described by Tonry & Schneider. A comparison of the HST results with the SBF distance moduli found by Ciardullo et al. shows significant disagreement and suggests that the rms error on these ground-based distance moduli is actually as large as +/-0.25mag. The agreement is only slightly improved when we compare our results with the HST and ground-based SBF distances from Ajhar et al. and Tonry et al.; the comparison suggests that a lower limit on the error of the HST SBF distance moduli is +/-0.17mag. 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.