Detection of surface brightness fluctuations in NGC 4373 using the Hubble Space Telescope

Surface brightness fluctuations (SBF) have been detected for three elliptic al galaxies-NGC 3379 in the Leo group, NGC 4406 in the Virgo cluster, and N GC 4373 in the Hydra-Centaurus supercluster-using marginally sampled, deep images taken with the Planetary Camera of the WFPC2 instrument on the Hubbl e Space Telescope (HST). The power spectrum of the fluctuations image is we ll fitted by an empirical model of the point-spread function constructed us ing point sources identified in the held. Comparison with high-quality grou nd-based observations of all three galaxies show excellent agreement in the measurement of the distance modulus over a substantial range in distance. This demonstrates the capability of the Planetary Camera of WFPC2 to measur e distances using the SBF technique despite the marginal sampling and small spatial coverage of the images. The residual variance due to unresolved so urces in all three galaxies is only 2%-5% of the detected fluctuations sign al, which confirms the advantage of HST imaging in minimizing the uncertain ty of this SBF correction. Extensive consistency checks, including an indep endent SBF analysis using an alternate software package, suggest that our i nternal uncertainties are <0.02 mag. The fluctuations magnitude for NGC 437 3 is I-F814W = 31.31 +/- 0.05 mag, corresponding to a distance modulus of ( m-M)(0) = 32.99 +/- 0.11. This implies a peculiar velocity for this galaxy of 415 +/- 330 km s(-1), which is smaller than derived from the D-n-sigma r elation.