A Search for Small-Scale Clumpiness in Dense Cores of Molecular Clouds

TL;DR

This study investigates small-scale clumpiness in dense cores of molecular clouds by analyzing spectral line profiles, revealing numerous unresolved clumps likely caused by turbulence, with implications for star formation processes.

Contribution

It provides the first detailed estimates of the number, size, density, and lifetime of unresolved small clumps in high-mass star-forming regions using spectral line analysis.

Findings

Detected ripples in line profiles suggest unresolved small clumps.

Estimated 20,000 to 300,000 clumps per region with densities of 3x10^5 to 10^6 cm^{-3}.

Clump lifetimes range from 10^4 to 10^5 years.

Abstract

We have analyzed HCN(1-0) and CS(2-1) line profiles obtained with high signal-to-noise ratios toward distinct positions in three selected objects in order to search for small-scale structure in molecular cloud cores associated with regions of high-mass star formation. In some cases, ripples were detected in the line profiles, which could be due to the presence of a large number of unresolved small clumps in the telescope beam. The number of clumps for regions with linear scales of ~0.2-0.5 pc is determined using an analytical model and detailed calculations for a clumpy cloud model; this number varies in the range: ~2 10^4-3 10^5, depending on the source. The clump densities range from ~3 10^5-10^6 cm^{-3}, and the sizes and volume filling factors of the clumps are ~(1-3) 10^{-3} pc and ~0.03-0.12. The clumps are surrounded by inter-clump gas with densities not lower than ~(2-7) 10^4 cm^{-3}. The internal thermal energy of the gas in the model clumps is much higher than their gravitational energy. Their mean lifetimes can depend on the inter-clump collisional rates, and vary in the range ~10^4-10^5 yr. These structures are probably connected with density fluctuations due to turbulence in high-mass star-forming regions.