The Gaia-ESO Survey: N-body modelling of the Gamma Velorum cluster

TL;DR

This study uses N-body simulations to model the Gamma Velorum cluster, explaining its two kinematically distinct populations as originating from two sub-clusters formed in separate star formation episodes.

Contribution

It presents a novel N-body simulation scenario that reproduces the observed kinematic and spatial features of the Gamma Velorum cluster's two populations.

Findings

The two populations originated from separate sub-clusters formed in different episodes.

Population B is strongly supervirial, while Population A is near virial equilibrium.

The model naturally explains the observed age difference and spatial separation.

Abstract

The Gaia-ESO Survey has recently unveiled the complex kinematic signature of the Gamma Velorum cluster: this cluster is composed of two kinematically distinct populations (hereafter, population A and B), showing two different velocity dispersions and a relative ~2 km s^-1 radial velocity (RV) shift. In this paper, we propose that the two populations of the Gamma Velorum cluster originate from two different sub-clusters, born from the same parent molecular cloud. We investigate this possibility by means of direct-summation N-body simulations. Our scenario is able to reproduce not only the RV shift and the different velocity dispersions, but also the different centroid (~0.5 pc), the different spatial concentration and the different line-of-sight distance (~5 pc) of the two populations. The observed 1-2 Myr age difference between the two populations is also naturally explained by our scenario, in which the two sub-clusters formed in two slightly different star formation episodes. Our simulations suggest that population B is strongly supervirial, while population A is close to virial equilibrium. We discuss the implications of our models for the formation of young star clusters and OB associations in the Milky Way.