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Date and Time of the Query: 2019-05-24 T21:48:46 PDT
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For refcode 2006A&A...458.1013M:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
2006A&A...458.1013M An I-band calibration of surface brightness fluctuation measurements at blue colours Mieske, S.; Hilker, M.; Infante, L. Abstract. Context: The surface brightness fluctuation (SBF) method is a powerful tool for deriving distances to galaxies for which single stars cannot be resolved. Up to now, the method has been calibrated mainly at red colours due to the intrinsic faintness of blue early-type galaxies. Aims: In this paper we address the I-band calibration of the SBF method at blue colours, the regime of dwarf elliptical galaxies (dEs). Methods: We present deep and wide-field VI photometry of the central Fornax cluster obtained at Las Campanas Observatory. With these data we perform an SBF analysis of 25 dEs in the range -16.5<M_V<-11.2 mag, 0.8<(V-I)_0<1.10 mag. Our colour calibration is accurate to better than 2%. For the calibration analysis we exclude eight dEs whose SBF measurement was affected by poor seeing ({FWHM} ~= 1"). Results: Our SBF data are inconsistent at the 3{sigma} level with a colour independent absolute SBF magnitude overline{M}_I, presenting a problem for SBF models that predict such a "flat" relation. There is a weak indication in our data (1.8{sigma}) to favour a two-branch calibration over a one-branch calibration with broad scatter in the overline{M}_I_ - (V-I) plane. We obtain the following one-branch empirical SBF calibration: overline{M}_I=-2.13 (+/- 0.17) + 2.44 (+/- 1.94) x [(V-I)_0_ - 1.00] mag. We deduce a 0.34 +/- 0.14 mag cosmic scatter of overline{M}_I, which is significantly larger than found at redder colours. This agrees with those theoretical SBF models that predict overline{M}_I_ is more sensitive to age-metallicity variations in the blue than in the red. We find evidence that the fainter galaxies in our samples contain younger and more metal-rich stellar populations than the brighter ones. The application of our empirical calibration to published SBF measurements of Hydra and Centaurus cluster dEs leaves the distances to both clusters unchanged. Key words: galaxies: clusters: individual: Fornax cluster, galaxies: dwarf, galaxies: distances and redshift, techniques:, photometric
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