Testing the surface brightness fluctuations method for dwarf elliptical galaxies in the Centaurus A group

We have obtained deep B and R-band CCD photometry for five dwarf elliptical galaxies that were previously identified on Schmidt films covering the reg ion of the Centaurus A (Cen A) group. From a Fourier analysis of the R-band CCD images we determined the surface brightness fluctuation (SBF) magnitud e (m) over bar(R) for each stellar system. All magnitudes are similar, and, given the small color spread, they suggest that these low surface brightne ss galaxies Lie approximately at the same distance, regardless of the assum ed SBF zero point. Long-slit spectra have been acquired to derive redshifts for two of the dwarfs, ESO 269-066 and ESO 384-016. The velocities, v. = 7 84 km s(-1) and v. = 561 km s(-1), respectively, identify them unambiguousl y as Cen A group members. An age (H delta(A))-metallicity (C-2 lambda 4668) analysis of the spectra reveals an underlying old and metal-poor stellar p opulation in both cases. Combining photometric and spectroscopic results we find strong evidence that indeed all dwarf galaxies are Cen A group member s. Based on Cepheid, TRGB, and PNLF distances published for the two main Ce n A group galaxies, NGC 5128 and NGC 5253, we adopted a mean group distance of 3.96 Mpc to calibrate the apparent fluctuation magnitudes. The resultin g absolute SBF magnitudes (M) over bar(R) of the dEs correlate with the der eddened colors (B-R)(0) as predicted by Worthey's stellar synthesis models, using the theoretical isochrones of Bertelli and collaborators. This good agreement allows a calibration of the SBF method for dwarf ellipticals in t he color range 0.8 < (B-R)(0) < 1.5. However, two branches of stellar popul ations appear in the (M) over bar(R)-color plane, and care has to be taken to decide which branch applies to a given observed dwarf. For dwarfs with ( B-R)(0) <1 there is very little color dependence ((M) over bar(R) approxima te to -1.2), in accord with our previous SBF analysis of faint, blue Sculpt or group dEs. For red dwarfs, (B - R)(0) > 1.2, the (M) over bar(R)-color r elation is steep, and accurate colors are needed to achieve SBF distances w ith an uncertainty of only 10%. One of the dwarfs, ESO 219-010, is located slightly behind the core of the Cen A group at about 4.8 Mpc, while the rem aining four recover the mean group distance of 3.96 Mpc that was put into t he calibration. The depth of the group is only 0.5 Ripe, which identifies t he Cen A group as a spatially well-isolated galaxy aggregate, in contrast t o the nearby Sculptor group.