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

TL;DR

This study analyzes the mass functions and structural properties of star clusters in NGC 1316, revealing how their evolution depends on density, location, and disruption processes, and suggesting the fate of second-generation globular clusters.

Contribution

It provides new insights into the formation and dynamical evolution of globular clusters in a merger remnant galaxy, linking their properties to initial conditions and environmental effects.

Findings

Mass peak of old clusters scales with internal density as rho_h^0.44.

Faint end of the luminosity function is affected by cluster radii exceeding tidal limits.

Most low-density red clusters in inner regions have been disrupted by tidal shocks.

Abstract

We study mass functions of globular clusters derived from HST/ACS images of the early-type merger remnant galaxy NGC 1316 which hosts a significant population of metal-rich globular clusters of intermediate age (~3 Gyr). For the old, metal-poor (`blue') clusters, the peak mass of the mass function M_p increases with internal half-mass density rho_h as (M_p proportional to rho_h^0.44) 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 > 9 kpc 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-rho_h tail of the initial distribution have already been destroyed in the inner regions of NGC 1316 by tidal shocking, and that several remaining low-rho_h 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.