Star Formation Patterns and Hierarchies

TL;DR

This paper discusses the hierarchical patterns of star formation across different scales, highlighting how large regions fragment into smaller structures, influencing star cluster formation and their observed properties.

Contribution

It provides a comprehensive overview of the hierarchical nature of star formation and explains how this hierarchy affects cluster efficiency and mass functions.

Findings

Star formation occurs in hierarchical space-time patterns.

Cluster positions and ages follow power law correlations.

Clusters often form in pairs at the lowest hierarchy level.

Abstract

Star formation occurs in hierarchical patterns in both space and time. Galaxies form large regions on the scale of the interstellar Jeans length and these large regions apparently fragment into giant molecular clouds and cloud cores in a sequence of decreasing size and increasing density. Young stars follow this pattern, producing star complexes on the largest scales, OB associations on smaller scales, and so on down to star clusters and individual stars. Inside each scale and during the lifetime of the cloud on that scale, smaller regions come and go in a hierarchy of time. As a result, cluster positions are correlated with power law functions, and so are their ages. At the lowest level in the hierarchy, clusters are observed to form in pairs. For any hierarchy like this, the efficiency is automatically highest in the densest regions. This high efficiency promotes bound cluster formation. Also for any hierarchy, the mass function of the components is a power law with a slope of around -2, as observed for clusters.