We measure F814W surface brightness fluctuations (SBFs) for a sample of distant shell galaxies with radial velocities ranging from 4000 to 8000 km s?1. 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 F814W versus (F 475W ? F 814W)0 calibration and we extend the previous M1 versus (B ? I)0 color 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?1 Mpc?1.
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