Published in "The Extragalactic Distance Scale", eds. M Livio, M. Donahue and N. Panagia, Cambridge University Press 1997.
Abstract. The globular cluster luminosity function (GCLF) for bright elliptical galaxies can be approximately represented as a Gaussian distribution, with a mean value M0V = -7.21 ± 0.26 mag and a width = 1.35 ± 0.05 mag. Most of the uncertainty in M0V is due to the Cepheid distance scale to the Virgo cluster used to determine the zeropoint. The intrinsic dispersion in M0V is 0.12 mag for bright ellipticals, making it competitive with the best distance indicators. The value of M0V appears to be nearly universal, with only a weak second-order dependence on luminosity clearly demonstrated and other second-order dependencies possible at about the 0.1 - 0.2 mag level (e.g. Hubble type, color, and environment). The Hubble Space Telescope provides a significant improvement in our ability to measure M0V, with limiting magnitudes for one orbit observations more than two magnitudes beyond the turnover in the GCLF for galaxies in the Virgo cluster. Historical estimates of the Hubble constant based on the GCLF have been surprisingly stable for nearly 30 years, with a mean H0 = 72 km s-1 Mpc-1. At present the best estimate can probably be determined using seven galaxies in the Fornax cluster, yielding a value of H0 = 82 ± 13 km s-1 Mpc-1. Several hundred high quality GCLF's should be published in the next few years, making globular clusters one of the most important distance indicators during the next decade.
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