Statistical fractal analysis of 25 young star clusters

TL;DR

This study uses statistical fractal analysis to examine the clustering and dynamical evolution of 25 young star clusters, revealing substructures, expansion, and consistency with supervirial models.

Contribution

It introduces a comprehensive fractal and statistical analysis approach to characterize clustering properties and dynamical states of young star clusters.

Findings

52% of clusters have substructures consistent with cloud fractal dimensions

Clusters with radial density profiles show increasing clustering parameter with surface density

All clusters are expanding and exhibit similar dynamical ages

Abstract

A large sample of young stellar groups is analysed aiming to investigate their clustering properties and dynamical evolution. A comparison of the Q statistical parameter, measured for the clusters, with the fractal dimension estimated for the projected clouds shows that 52% of the sample has substructures and tends to follow the theoretically expected relation between clusters and clouds, according to calculations for artificial distribution of points. The fractal statistics was also compared to structural parameters revealing that clusters having radial density profile show a trend of parameter s increasing with mean surface stellar density. The core radius of the sample, as a function of age, follows a distribution similar to that observed in stellar groups of Milky Way and other galaxies. They also have dynamical age, indicated by their crossing time that is similar to unbound associations. The statistical analysis allowed us to separate the sample into two groups showing different clustering characteristics. However, they have the same dynamical evolution, since the whole sample has been revealed as expanding objects, for which the substructures seem to have not been erased. These results are in agreement with simulations that adopt low surface densities and models under supervirial conditions.