Does sub-cluster merging accelerate mass segregation in local star formation?

TL;DR

This study investigates how merging sub-clusters influence rapid mass segregation in star formation, showing that such mergers can produce compact massive star configurations consistent with observations and simulations.

Contribution

It demonstrates that sub-cluster merging accelerates mass segregation in local star formation, extending previous models to more typical cluster sizes and conditions.

Findings

Merging sub-clusters can produce compact massive star configurations.

Sub-virial initial conditions can mimic mass segregation effects.

The modified minimum spanning tree technique aids in analyzing mass segregation.

Abstract

The nearest site of massive star formation in Orion is dominated by the Trapezium subsystem, with its four OB stars and numerous companions. The question of how these stars came to be in such close proximity has implications for our understanding of massive star formation and early cluster evolution. A promising route toward rapid mass segregation was proposed by McMillan et al. (2007), who showed that the merger product of faster-evolving sub clusters can inherit their apparent dynamical age from their progenitors. In this paper we briefly consider this process at a size and time scale more suited for local and perhaps more typical star formation, with stellar numbers from the hundreds to thousands. We find that for reasonable ages and cluster sizes, the merger of sub-clusters can indeed lead to compact configurations of the most massive stars, a signal seen both in Nature and in large-scale hydrodynamic simulations of star formation from collapsing molecular clouds, and that sub-virial initial conditions can make an un-merged cluster display a similar type of mass segregation. Additionally, we discuss a variation of the minimum spanning tree mass-segregation technique introduced by Allison et al. (2009).