A Statistical Study of Massive Cluster-Forming Clumps

TL;DR

This study investigates the physical and chemical properties of massive molecular clumps associated with star clusters, revealing evolutionary stages and dynamics of cluster formation through statistical analysis of observational data.

Contribution

It provides a new classification scheme for cluster-forming clumps based on spatial correlation and chemical composition, offering insights into their evolution.

Findings

Clumps with clusters have typical mass ~10^3 Mo, radius ~0.5 pc, density ~10^5 cm^-3.

Clump evolution proceeds from Type 1 to Type 4, with infall motions observed in some Type 2 clumps.

Type 1 clumps are older and more stable, likely supported by strong magnetic fields.

Abstract

We report results of the observations of 15 regions in several molecular lines for a statistical study of massive cluster-forming clumps. We identified 24 clumps based on the C18O (J=1-0) data obtained by the NRO 45 m telescope, and found that 16 of them are associated with young clusters. The clumps associated with clusters have a typical mass, radius, and molecular density of ~1 X 10^3 Mo, ~0.5 pc, ~1 X 10^5 cm^-3, respectively. We categorized the clumps and clusters into four types according to the spatial coincidence of gas and star density, and discussed their evolutions: Clumps without clusters (Type 1), clumps showing good correlations with clusters (Type 2), clumps showing poor correlations with clusters (Type 3), and clusters with no associated clumps (Type 4). Analyses of the velocity structures and the chemical compositions imply that the clump + cluster systems should evolve from Type 1 to Type 4. We found that some of the Type 2 clumps are infalling on the clump-scale to form clusters at the clump center, which should commonly occur in the beginning of cluster formation. Interestingly, all of the identified Type 1 clumps are likely to be older than the Type 2 clumps in terms of chemical compositions, suggesting that they have been gravitationally stable for a long time possibly being supported by the strong magnetic field of > 1 mG.Type 1 clumps younger than the observed Type 2 clumps should be very rare to find because of their short lifetime.