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The dynamics of infrared dark hubs and the formation of massive stars

Anderson, Michael ORCID: 2023. The dynamics of infrared dark hubs and the formation of massive stars. PhD Thesis, Cardiff University.
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Hub-filament systems (HFSs) are networks of converging interstellar filaments, often with active star formation at their centres, that may play an important role in high-mass star formation. In this thesis, I have studied a sample of six HFSs observed with ALMA 2.9mm continuum and N2H+(J=1–0) molecular line emission to investigate their physical and dynamical properties. The first part of this research project was to investigate the how much of their mass is contained within cores, and with a broader sample of clumps, whether their morphology plays a part in what fraction of their mass is locked up in their most massive core. I showed that this fraction is significantly higher in IR-dark hubs than IR-bright clumps, suggesting that the most-massive cores form early on. In the second project, I investigated the kinematic and dynamical properties of these six HFSs using the dense gas tracer N2H+. The data show intricate emission structures, and in total contain around 180,000 spectra, with a high fraction of them appearing very complex. At the time there was no programme that could automatically fit such complex spectra en masse. As a consequence I led the development of mwydyn, a fully-automated, multiple velocity component, hyperfine line-fitting code. Results from this code revealed that the emission invariably consists of quiescent individual filaments in the outskirts that converge towards dynamically active hub centres, where a systematic increase in velocity dispersion and number of velocity components is observed, which I suggest could be the result of an accretion shock at the filament-hub intersection, or complex unresolved gas flows within the hub. Also, despite the masses of the HFSs spanning over an order of magnitude, the distributions of their velocity centroid are remarkably similar. I propose that this could be a sign that these HFSs are sheet-like structures seen mostly face-on. However, in order to draw robust conclusions it is clear that further investigation is required with a much larger, unbiased sample of clumps covering a broad range of masses, evolutionary stage, and morphology.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Physics and Astronomy
Subjects: Q Science > QC Physics
Uncontrolled Keywords: astrophysics, star formation, interstellar medium (ISM), high-mass stars, hub-filament systems (HFS), molecular clouds, observational astronomy, interferometry, ALMA
Funders: STFC
Date of First Compliant Deposit: 30 May 2024
Last Modified: 30 May 2024 13:42

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