2008ApJ...678..168B

We measure F814W surface brightness fluctuations (SBFs) for a sample of distant shell galaxies with radial velocities ranging from 4000 to 8000 km/s. The distance at galaxies is then evaluated by using the SBF method. For this purpose, theoretical SBF magnitudes for the HST ACS filters are computed for single-burst stellar populations covering a wide range of ages (t=1.5-14 Gyr) and metallicities (Z=0.008-0.04). Using these stellar population models, we provide the first M{d1}_F814W versus (F475W-F814W)₀ calibration and we extend the previous M₁ versus (B-I)₀color relation to colors (B-I)₀≤2.0 mag. Coupling our SBF measurements with the theoretical calibration we derive distances with a statistical uncertainty of ∼8%, and systematic error of ∼6%. The procedure developed to analyze data ensures that the indetermination due to possible unmasked residual shells is well below ∼12%. The results suggest that optical SBFs can be measured at d≥100 Mpc with HST ACS imaging. SBF-based distances coupled with recession velocities corrected for peculiar motion, allow us obtain H₀=76±6 (statistical) ±5 (systematic) km/s/Mpc.