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

Abstract

The dynamical evolution of the globular cluster systems in external galaxies is estimated, based on the standard dynamical theory normalized to the Milky Way. Assuming the same initial luminosity function, we construct an intrinsic distribution of globular clusters resulting from an isolated, passive evolution over the Hubble time of the true initial distribution. The galactic environment changes this distribution primarily through tidal shocks and dynamical friction. Our model explains, on a quantitative basis, the observed differences between the inner and outer populations of globular clusters in the Galaxy, M31, and M87. We can further calculate the amount of apparent brightening of the peak of the luminosity function due to destruction of low-mass clusters. Comparing the corrected peak with the center of the intrinsic distribution, we obtain distance moduli to the galaxies. Using this method we find dmM31 = 24.03 +/- 0.23 and dmM87 = 30.81 +/- 0.17, as compared to the current best estimates using other methods (dmM31 = 24.30 +/- 0.20, dmM87 = 31.0 +/- 0.1). This new method, coupled with Hubble Space Telescope observations, promises to provide an independent way of estimating distances to galaxies with recessional velocities