Sizes, half-mass densities, and mass functions of star clusters in the merger remnant NGC 1316: Clues to the fate of second-generation globular clusters

Abstract

We study mass functions of globular clusters derived from Hubble Space Telescope/Advanced Camera for Surveys images of the early-type merger remnant galaxy NGC 1316, which hosts a significant population of metal-rich globular clusters of intermediate age (3Gyr). For the old, metal-poor ("blue") clusters, the peak mass of the mass function increases with internal half-mass density ρh as , whereas it stays approximately constant with galactocentric distance R gal. The mass functions of these clusters are consistent with a simple scenario in which they formed with a Schechter initial mass function and evolved subsequently by internal two-body relaxation. For the intermediate-age population of metal-rich ("red") clusters, the faint end of the previously reported power-law luminosity function of the clusters with R gal > 9kpc is due to many of those clusters having radii larger than the theoretical maximum value imposed by the tidal field of NGC 1316 at their R gal. This renders disruption by two-body relaxation ineffective. Only a few such diffuse clusters are found in the inner regions of NGC 1316. Completeness tests indicate that this is a physical effect. Using comparisons with star clusters in other galaxies and cluster disruption calculations using published models, we hypothesize that most red clusters in the low-ρh tail of the initial distribution have already been destroyed in the inner regions of NGC 1316 by tidal shocking, and that several remaining low-ρh clusters will evolve dynamically to become similar to "faint fuzzies" that exist in several lenticular galaxies. Finally, we discuss the nature of diffuse red clusters in early-type galaxies. © 2012. The American Astronomical Society. All rights reserved.