THE LUMINOSITY DISTRIBUTION OF GLOBULAR-CLUSTERS IN 3 GIANT VIRGO ELLIPTICALS

We present CCD photometry in B for the globular clusters around three of the "normal" ellipticals in Virgo, NGC 4365, NGC 4472, and NGC 4649. These new data define the luminosity distributions of the clusters to a limit B = 26.2 and clearly reach past the peak frequency (turnover point). The turnover magnitudes in these three systems and in M87 average <B0> = 24.77 with a +/- 0.2 mag galaxy-to-galaxy scatter, and the functions match a Gaussian distribution with dispersion sigma(B) = 1.46 +/- 0.07 mag. Our results indicate that the globular clusters in giant ellipticals follow similar luminosity distributions and support their use as standard candles for more distant galaxies of the same type. Fitting our composite Virgo globular cluster luminosity function to the Milky Way cluster distribution yields an estimated Virgo distance modulus (m - M)B = 31.5 +/- 0.25; hence H0 congruent-to 70 km s-1 Mpc-1. This result must remain provisional until the intrinsic turnover luminosity difference DELTA-M(B)0 between the Local Group spirals and the giant ellipticals can be calibrated self-consistently. We find no detectable changes in the GCLF parameters with galactocentric radius, for our measured region (0.'7 < r < 2.'5). In each galaxy there is evidence for a core radius in the cluster system (a flattening of the radial density distribution) within r congruent-to 1'. In NGC 4472 and NGC 4649, the clusters follow a distinctly more extended distribution than the halo light.