Disruption of Star Clusters in the Interacting Antennae Galaxies

TL;DR

This study shows that the decline in star cluster numbers in the Antennae Galaxies is primarily due to their disruption over time, rather than changes in their formation rate, aligning with patterns seen in calmer galaxies.

Contribution

It demonstrates that cluster disruption, rather than formation rate variations, explains the observed age distribution in the Antennae Galaxies, using combined simulations and models.

Findings

Cluster disruption accounts for the observed age distribution.

Formation rates vary slowly over the past 100 million years.

The disruption timescale in the Antennae resembles that in quiescent galaxies.

Abstract

We reexamine the age distribution of star clusters in the Antennae in the context of N-body+hydrodynamical simulations of these interacting galaxies. All of the simulations that account for the observed morphology and other properties of the Antennae have star formation rates that vary relatively slowly with time, by factors of only 1.3 - 2.5 in the past 10^8 yr. In contrast, the observed age distribution of the clusters declines approximately as a power law, dN/dt \propto t^{gamma} with gamma = -1.0, for ages 10^6 yr \la t \la 10^9 yr. These two facts can only be reconciled if the clusters are disrupted progressively for at least 10^8 yr and possibly 10^9 yr. When we combine the simulated formation rates with a power-law model, f_surv \propto t^{delta}, for the fraction of clusters that survive to each age t, we match the observed age distribution with exponents in the range -0.9 \la delta \la -0.6 (with a slightly different delta for each simulation). The similarity between delta and gamma indicates that dN/dt is shaped mainly by the disruption of clusters rather than variations in their formation rate. Thus, the situation in the interacting Antennae resembles that in relatively quiescent galaxies such as the Milky Way and the Magellanic Clouds.