Detection of Radial Surface Brightness Fluctuation and Color Gradients   in elliptical galaxies with ACS
  We study surface brightness fluctuations (SBF) in a sample of 8 elliptical galaxies using Advanced Camera for Surveys (ACS) Wide Field Channel (WFC) data drawn from the Hubble Space Telescope (HST) archive. SBF magnitudes in the F814W bandpass, and galaxy colors from F814W, F435W, and F606W images -- when available -- are presented. Galaxy surface brightness profiles are determined as well. We present the first SBF--broadband color calibration for the ACS/WFC F814W bandpass, and (relative) distance moduli estimates for 7 of our galaxies.   We detect and study in detail the SBF variations within individual galaxies as a probe of possible changes in the underlying stellar populations. Inspecting both the SBF and color gradients in comparison to model predictions, we argue that SBF, and SBF-gradients, can in principle be used for unraveling the different evolutionary paths taken by galaxies, though a more comprehensive study of this issue would be required. We confirm that the radial variation of galaxy stellar population properties should be mainly connected to the presence of radial chemical abundance gradients, with the outer galaxy regions being more metal poor than the inner ones. 
Michele Cantiello (1), John P. Blakeslee (2), Gabriella Raimondo (1),   Simona Mei (2), Enzo Brocato (1), Massimo Capaccioli...