High-fidelity view of the structure and fragmentation of the high-mass, filamentary IRDC G11.11-0.12

TL;DR

This study provides a detailed analysis of the internal structure and fragmentation of the high-mass filamentary IRDC G11.11-0.12 using novel high-resolution dust mapping techniques, revealing its dense gas properties and hierarchical fragmentation behavior.

Contribution

It introduces two independent, high-resolution dust mapping methods and applies them to analyze the structure and fragmentation of a high-mass filamentary cloud, offering new insights into its mass distribution and stability.

Findings

G11 has a top-heavy mass distribution and high linear mass density.

Fragmentation at scales 0.5-8 pc aligns with a self-gravitating cylinder model.

Smaller scales (<0.5 pc) show fragmentation consistent with spherical Jeans instability.

Abstract

Star formation in molecular clouds is intimately linked to their internal mass distribution. We present an unprecedentedly detailed analysis of the column density structure of a high-mass, filamentary molecular cloud, namely IRDC G11.11-0.12 (G11). We use two novel column density mapping techniques: high-resolution (FWHM=2", or ~0.035 pc) dust extinction mapping in near- and mid-infrared, and dust emission mapping with the Herschel satellite. These two completely independent techniques yield a strikingly good agreement, highlighting their complementarity and robustness. We first analyze the dense gas mass fraction and linear mass density of G11. We show that G11 has a top heavy mass distribution and has a linear mass density (M_l ~ 600 Msun pc^{-1}) that greatly exceeds the critical value of a self-gravitating, non-turbulent cylinder. These properties make G11 analogous to the Orion A cloud, despite its low star-forming activity. This suggests that the amount of dense gas in molecular clouds is more closely connected to environmental parameters or global processes than to the star-forming efficiency of the cloud. We then examine hierarchical fragmentation in G11 over a wide range of size-scales and densities. We show that at scales 0.5 pc > l > 8 pc, the fragmentation of G11 is in agreement with that of a self-gravitating cylinder. At scales smaller than l < 0.5 pc, the results agree better with spherical Jeans' fragmentation. One possible explanation for the change in fragmentation characteristics is the size-scale-dependent collapse time-scale that results from the finite size of real molecular clouds: at scales l < 0.5 pc, fragmentation becomes sufficiently rapid to be unaffected by global instabilities.