The Globular Cluster Luminosity Function as a Distance Indicator: Dynamical Effects

The dynamical evolution of the globular cluster systems in galaxies ispredicted, based on the standard dynamical theory normalized to the example ofthe Milky Way. The major processes varying with the galactocentric distance arethe tidal shocks and dynamical friction. Our simple model explains, on aquantitative basis, the observed differences of the inner and outer populationsof globular clusters. We can thus calculate corrections for dynamical evolutionfor the luminosity function of globular clusters with the assumption that theinitial luminosity function is identical in all galaxies (and we can test thisassumption as well, in certain cases). Then we can compute the expecteddistribution of absolute magnitudes and compare it with the observeddistribution of apparent magnitudes to estimate the distance moduli for M31 andM87. Using this new method we find dm(M31)=24.05 +- 0.23, dm(M87)=30.83 +-0.17, as compared to current best estimates using other methods ofdm(M31)=24.30 +- 0.20, dm(M87)=31.0 +- 0.1. As a check on the method wecompute, and compare with observations, the differences between the inner andouter globular clusters in all three galaxies. This new method, coupled withHST observations, promises to provide an independent method of estimatingdistances to galaxies with recession velocities < 10,000 km/s, or D < 100 Mpc.Comment: 12 pages, 2 figures; submitted to ApJ Letter