M87, Globular Clusters, and Galactic Winds: Issues in Giant Galaxy Formation

We have used the high-resolution camera at the Canada-France-Hawaii Telescope to obtain VRI photometry of the globular clusters in the innermost 140 arcsec of the M87 halo. The results are used to discuss several issues concerning the formation and evolution of globular cluster systems in supergiant elliptical galaxies like M87. Our principal results are as follows: (1) From our deep R-band photometry of the cluster population, we find no significant change in the globular cluster luminosity function (GCLF) with galactocentric radius, for cluster masses greater than M 100,00 solar masses. This result places constraints on current theoretical predictions of the rate of cluster evolution by tidal shocking and evaporation, indicating that the main effects of dynamical evolution may be felt only on lower mass clusters that are below the faint limit of most current observations. (2) We derive the metallicity gradient and mean metallicity of the clusters from r = 9 arcsec out to r about 500 arcsec. Within the core radius r(c) = 1 arcmin of the globular cluster system, the metallicity distribution is uniform, but at larger radii the mean metallicity declines steadily as Z/Z(solar) about r exp -0.9. (3) The various options for explaining the existence of high specific frequency galaxies like M87 are evaluated. We offer a new explanation for the large observed S(N) range among the brightest cluster elliptical galaxies. (Author)