On Filaments within Molecular Clouds and their Connection to Star Formation

TL;DR

This study investigates the evolution, fragmentation, and observational signatures of filaments in molecular clouds, revealing that filament fragmentation is driven by colliding flows rather than gravitational instability, and that dust observations alone cannot determine filament inclination.

Contribution

It provides a comprehensive analysis of filament evolution within molecular clouds using simulations and radiative transfer, highlighting the limitations of simple models and the complexity of filament fragmentation processes.

Findings

Filaments fragment below the critical line mass due to colliding flows.

Dust observations alone cannot determine filament inclination or 3D structure.

Fragmentation is not solely driven by gravitational instability.

Abstract

In recent years, there were studies on the omnipresence and structures of filaments in star-forming regions, and the role of their fragmentation in the process of star formation. However, only a few studies analysed the evolution of filaments and their distribution with the Galactic disk where filaments form self-consistently as part of large-scale molecular cloud evolution. In this thesis, I perform dust radiative transfer calculations to study the effect of inclination on dust observations of filaments to evaluate whether the variations enable the identification of more filaments within dust surveys. I address the early evolution of pc-scale filaments that form within individual clouds and focus on how and when the filaments fragment, and how the fragmentation relates to typically used observables. For evaluating the equilibrium state of filaments and the nature of their fragmentation I examine three simulated molecular clouds formed in kpc-scale numerical simulations modelling a self-gravitating, magnetised, stratified, supernova-driven ISM. The first fragments appear when the line masses of the simulated filaments lie well below the critical line mass of Ostrikers isolated hydrostatic equilibrium solution. This indicate that, although the turbulence of the entire clouds is mostly driven by gravitational contraction, fragmentation does not occur do to gravitational instability, but is supported by colliding flow motions. I conclude that there is no single quantity in my analysis that can uniquely trace the inclination and 3D structure of a filament based on dust observations alone. A simple model of an isolated, isothermal cylinder may not provide a good approach for fragmentation analysis, independently of the dominant driving source of the parental cloud.