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Abstract

We present observations of the surface-brightness fluctuations of M32, NGC 3379, and 13 Virgo Cluster galaxies in the V, R, and I photometric bands. The scatter in m^bar^_I_ that we observe among the Virgo galaxies is consistent with the depth of the cluster, which implies the fluctuation luminosity in the I band is quite insensitive to stellar population differences, and that we are resolving the Virgo Cluster front to back. We find that NGC 4365 is behind Virgo in the W cloud, and NGC 4468 and NGC 4489 are in the foreground. We estimate that our relative distances may be as good as 3% for an individual galaxy, and we compare our distances with those obtained with planetary nebulae luminosity functions and with D_n_ -σ. Computation of M^bar^ for a large grid of Yale isochrones shows that M^bar^_I_ is expected to be insensitive to metallicity and age, and that other wavelengths yield information about stellar population parameters. However, if we assume a distance to M32 to 0.7 Mpc, we encounter a discrepancy in that M^bar^_I_ from the isochrones is 45% brighter than m^bar^_I_ measured for M32. We prefer the empirical calibration of shifting M^bar^_I_ from the isochrones to relieve this disagreement. Using this empirical calibration, we obtain an average distance to the Virgo Cluster of 17+/-1 Mpc, which implies a Hubble constant of 78+/-6 km/s/Mpc. If we use the isochrone calibration directly, we obtain 21 Mpc and H_0_ = 64+/-5 km/s/Mpc. We compare our "fluctuation colors" (V^bar^-R^bar^) and (R^bar^-I^bar^) with the isochrones and conclude that no single isochrone can match the stellar population in these galaxies, and that there must be a spread in metallicity. A comparison of (V^bar^-I^bar^) with the Mg_2_ index suggests the possibility of detecting recent star formation.

Observations of surface-brightness fluctuations in Virgo

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