Deep Luminosity Functions of Old and Intermediate-Age Globular Clusters in NGC 1316: Evidence for Dynamical Evolution of Second-Generation Globular Clusters

The Advanced Camera for Surveys on board the Hubble Space Telescope has beenused to obtain deep high-resolution images of the giant early-type galaxy NGC1316 which is an obvious merger remnant. These observations supersede previous,shallower observations which revealed the presence of a population ofmetal-rich globular clusters of intermediate age (~ 3 Gyr). We detect a totalof 1496 cluster candidates, almost 4 times as many as from the previous WFPC2images. We confirm the bimodality of the color distribution of clusters, evenin V-I, with peak colors 0.93 and 1.06. The large number of detected clustersallows us to evaluate the globular cluster luminosity functions as a functionof galactocentric radius. We find that the luminosity function of the inner 50%of the intermediate-age, metal-rich (`red') population of clusters differsmarkedly from that of the outer 50%. In particular, the luminosity function ofthe inner 50% of the red clusters shows a clear flattening consistent with aturnover that is about 1.0 mag fainter than the turnover of the blue clusters.This constitutes the first direct evidence that metal-rich cluster populationsformed during major mergers of gas-rich galaxies can evolve dynamically(through disruption processes) into the red, metal-rich cluster populationsthat are ubiquitous in `normal' giant ellipticals.Comment: Accepted for publication in ApJ Letters; 4 pages in emulateapj style. 3 figure