Disruption of Star Clusters in the Interacting Antennae 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/dτ ∝ τ γ with γ = −1.0, for ages 10 6 yr τ 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 ∝ τ δ , for the fraction of clusters that survive to each age τ , we match the observed age distribution with exponents in the range −0.9 δ −0.6 (with a slightly different δ for each simulation). The similarity between δ and γ indicates that dN/dτ 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.

X-Ray Binaries and Star Clusters in the Antennae: Optical Cluster Counterparts

“…Linden et al (2010) show in their Figure 1 that in solar metallicity systems like the Antennae, bright (L X > 10 36 erg s −1 ) HMXBs turn on suddenly at ages of approximately 4 Myr, with a production rate that is sharply peaked between 4 and 6 Myr and dropping off thereafter. These ages are quite similar to those listed in Table 1 for many coincident clusters, and are probably not due to a peak in the star formation rate 4-6 Myr ago, since (1) dynamical simulations which reproduce the observed morphology of the merging Antennae do not find such a peak in the star formation rate (see, e.g., Karl et al 2011), and (2) it would be impossible to have such a well-timed burst over the entire field of the Antennae since the communication time is ∼10 9 yr for a signal traveling at the typical random velocity of the interstellar medium of ≈10 km s −1 (e.g., Fall et al 2009;Whitmore et al 2007). Hence, our age analysis is consistent with predictions for the production timescale of HMXBs in high-metallicity galaxies.…”

A parsec-resolution simulation of the Antennae galaxies: formation of star clusters during the merger

“…The best match with observations being reached at t = 152 Myr, we note that the SFR has declined and increased again before reaching the present day, by a factor up to ∼ 3 during the last 100 Myr, which contradicts the assumption of a constant SFR made by Karl et al (2011) to interpret the observed age distribution of clusters in the Antennae. A longer time-lapse between the pericenter passages would allow the SFR to reach a relatively constant value after the first starburst and would thus be more consistent with the assumption of Karl et al (2011). In our simulation, the SFR averaged over the last 100 Myr is higher than the presentday value.…”

Star Cluster Formation and Destruction in the Merging Galaxy NGC 3256

“…Unfortunately, to our knowledge, there is no published SFH for the merging, starbursting NGC 3256 system, either from direct observations or from high quality simulations. If the SFH of NGC 3256 has been constant to within a factor of a few over this timescale, as suggested by some simulations for the starbursting Antennae galaxies (Karl, Fall, & Naab 2011), as well as observational works on interacting galaxies (e.g., Knapen, Cisternas, & Querejeta 2015 and references therein), then the clusters in NGC 3256 would also have a disruption history similar to that found in these more quiescent galaxies.…”