Star Cluster Formation from Turbulent Clumps. III. Across the mass spectrum

TL;DR

This study models the formation and early evolution of star clusters across a broad mass spectrum, revealing how initial conditions influence cluster density, binary properties, and dynamical ejections, with implications for observed stellar populations.

Contribution

It introduces a comprehensive model of star cluster formation from turbulent gas clumps across various masses and densities, highlighting the impact of initial conditions on cluster evolution.

Findings

Higher mass, lower density clumps form denser cluster cores.

Dynamical evolution leads to higher bound fractions in more massive clusters.

Binary properties and stellar ejections vary systematically with initial conditions.

Abstract

We study the formation and early evolution of star clusters that have a wide range of masses and background cloud mass surface densities, $\Sigma_{\rm cloud}$, which help set the initial sizes, densities, and velocity dispersions of the natal gas clumps. Initial clump masses of 300, $3,000$ and $30,000$ $M_\odot$ are considered, from which star clusters are born with an assumed 50% overall star formation efficiency and with 50% primordial binarity. This formation is gradual, i.e., with a range of star formation efficiencies per free-fall time from 1% to 100%, so that the formation time can range from 0.7 Myr for low-mass, high-$\Sigma_{\rm cloud}$ clumps to $\sim30$ Myr for high-mass, low-$\Sigma_{\rm cloud}$ clumps. Within this framework of the Turbulent Clump model, for a given $\Sigma_{\rm cloud}$, clumps of higher mass are of lower initial volume density, but their dynamical evolution leads to higher bound fractions and causes them to form much higher density cluster cores and maintain these densities for longer periods. This results in systematic differences in the evolution of binary properties, degrees of mass segregation and rates of creation of dynamically ejected runaways. We discuss the implications of these results for observed star clusters and stellar populations.