The long-term evolution of star clusters formed with a centrally-peaked star-formation-efficiency profile

TL;DR

This study investigates the long-term evolution and dissolution times of star clusters with different star formation efficiencies, revealing how initial conditions influence cluster longevity and structural properties in the solar neighborhood.

Contribution

It combines a local-density-driven formation model with N-body simulations to analyze the impact of star formation efficiency on cluster evolution and dissolution.

Findings

High-SFE clusters follow a tight mass-dependent dissolution relation.

Low-SFE clusters show large scatter and a shallower relation.

The combined model matches observed cluster dissolution times in the solar neighborhood.

Abstract

We have studied the long-term evolution of star clusters of the solar neighborhood, starting from their birth in gaseous clumps until their complete dissolution in the Galactic tidal field. We have combined the "local-density-driven cluster formation model" of Parmentier & Pfalzner (2013) with direct N-body simulations of clusters following instantaneous gas expulsion. We have studied the relation between cluster dissolution time, $t_{dis}$, and cluster "initial" mass, $M_{init}$, defined as the cluster {mass at the end of the dynamical response to gas expulsion (i.e. violent relaxation), when the cluster age is 20-30 Myr}. We consider the "initial" mass to be consistent with other works which neglect violent relaxation. The model clusters formed with a high star formation efficiency (SFE -- i.e. gas mass fraction converted into stars) follow a tight mass-dependent relation, in agreement with previous theoretical studies. However, the low-SFE models present a large scatter in both the "initial" mass and the dissolution time, and a shallower mass-dependent relation than high-SFE clusters. Both groups differ in their structural properties on the average. Combining two populations of clusters, high- and low-SFE ones, with domination of the latter, yields a cluster dissolution time for the solar neighborhood in agreement with that inferred from observations, without any additional destructive processes such as giant molecular cloud encounters. An apparent mass-independent relation may emerge for our low-SFE clusters when we neglect low-mass clusters (as expected for extra-galactic observations), although more simulations are needed to investigate this aspect.