A cluster in the making: ALMA reveals the initial conditions for high-mass cluster formation

TL;DR

This study uses ALMA observations to analyze the initial conditions of high-mass cluster formation in G0.253+0.016, revealing complex hierarchical gas structures shaped by turbulence, which may evolve into a dense star cluster.

Contribution

It provides high-resolution ALMA data showing the turbulent, hierarchical gas structures in a potential high-mass cluster progenitor, highlighting the transition scale where gravity dominates.

Findings

Turbulence influences gas structure at ~0.1 pc scale.

Gas distribution is extended and hierarchical, not centrally condensed.

A break in the turbulent power spectrum suggests gravity overcomes thermal pressure at ~0.1 pc.

Abstract

G0.253+0.016 is a molecular clump that appears to be on the verge of forming a high mass, Arches-like cluster. Here we present new ALMA observations of its small-scale (~0.07 pc) 3mm dust continuum and molecular line emission. The data reveal a complex network of emission features, the morphology of which ranges from small, compact regions to extended, filamentary structures that are seen in both emission and absorption. The dust column density is well traced by molecules with higher excitation energies and critical densities, consistent with a clump that has a denser interior. A statistical analysis supports the idea that turbulence shapes the observed gas structure within G0.253+0.016. We find a clear break in the turbulent power spectrum derived from the optically thin dust continuum emission at a spatial scale of ~0.1 pc, which may correspond to the spatial scale at which gravity has overcome the thermal pressure. We suggest that G0.253+0.016 is on the verge of forming a cluster from hierarchical, filamentary structures that arise from a highly turbulent medium. Although the stellar distribution within Arches-like clusters is compact, centrally condensed and smooth, the observed gas distribution within G0.253+0.016 is extended, with no high-mass central concentration, and has a complex, hierarchical structure. If this clump gives rise to a high-mass cluster and its stars are formed from this initially hierarchical gas structure, then the resulting cluster must evolve into a centrally condensed structure via a dynamical process.